One type of passive buzzer requires only a ground and signal. A second type requires a ground, signal, and Vcc.
As I am writing a lesson, I want to make sure that I am using the correct terminology. What is the correct way to reference the second type, the one that also requires Vcc?
Good Luck, I call one a piezo speaker and the other a piezo buzzer. I am not sure if I am correct but the speaker needs a AC/pulsing signal( can be varying frequency), the buzzer generally uses a DC signal. Try this search term: "what is the difference between a piezo buzzer and piezo speaker"
Technically, a "buzzer" should be active. You apply DC voltage and it makes a sound. And usually a "beep" or a "tone" rather than a "buzz". 
A passive piezo device can be called a "transducer" or "speaker". There are piezo tweeters. A piezo transducer can also be used as a microphone or vibration sensor. Some cheap phono pickups (for playing vinyl records) are piezoelectric and they are usually called "ceramic" pickups.
I don't think I've ever seen one with 3 terminals!
Modules maybe(?)
In my understanding the 2-wire versions are passive speakers while the 3-wire versions are active buzzers with a built-in fixed frequency generator.
That is the part I am looking at. The vendors call it a passive buzzer, but it needs Vcc, GNG, and Signal.
No, this style will not make a sound if Vcc is applied to the Signal input. It needs a PWM signal, like the passive buzzer.
I thought this would be an easy one, I think I am going to go with plan A and call it a driven passive buzzer.
Every component can be "driven".
Just a "passive buzzer" or a "passive buzzer with only a piezo disc" or something like that.
They say that a picture is worth a thousand words, so how about a picture of a open passive buzzer ?
That's the definition of a passive buzzer, that it needs a frequency signal. Active buzzers have a fixed frequency and only can be turned on or off.
In so far the number of pins/wires is unimportant.
That part is a buzzer module. The buzzer on it can be either passive or active and the number of pins of the module don't say anything about it, as DrDiettrich just said.
So, The explanation is something like this (note, this is not a full script, it is just an outline):
This is a Passive Buzzer. You will note that only two of the pins are labelled. The pin labelled - will connect to GND and the pin labelled S, or "Signal," will connect to a PWM pin on your Arduino. The centre pin does not need to be connected to anything but can be connected to 3V-5Vdc. This component is simply a stand-alone passive buzzer attached to a small board with a header, to make it easier to use with our breadboard.
This is a Passive Buzzer Module, which you will sometimes hear me call a driven passive buzzer in an attempt to make it clear which of the two devices I am talking about.
The Passive Buzzer Module differs from the Passive Buzzer in that it is a bit louder, and it needs three wires. The one labelled GND will go to GND. The one labelled I/O will still go to a PWM pin. Here is the difference, the pin labeled Vcc needs to go to 5V.
emphasized textEnd of script
Is this correct? The reality is that I didn't notice the difference when I ordered, the supplier just called it a passive buzzer. I saw that and ordered 25.
To give a bit more context, this is a Title I middle school (Title I is eduCode for "Poverty") the students are mostly in 8th grade with some 7th grade students. The students are at least half ESL (English as a second language), and based on state testing, over half of them. . . I know the numbers, close to 80% of them are not at grade level. This is an "advanced" elective class.
My certification, which is applicable to this class, is in Education Technology. Normally that is a Shop teacher cert. The class falls under the Computer and Engineering curriculum. We have had a major restructuring of how often Elective teachers see their students so I am adding this module to the class. So far the reaction of the students, who are still doing spreadsheets (A great place to introduce the IF statement), is very positive. If you have access to Canvas Commons (the teacher side) I can share the course, up to where I am at, with you.
This information is not correct (Edited after post #17). Take a look in the Keyestudio Passive Buzzer docs here: https://wiki.keyestudio.com/Ks0019_keyestudio_Passive_Buzzer_module
Or active buzzer here: https://www.keyestudio.com/products/free-shipping-keyestudio-active-buzzer-alarm-module-for-arduino
The difference from the module to the standalone buzzer is that the module contains other electronic parts (resistors, voltage converters...) to make it easier to use.
Interesting point, I changed the script. However, I am not sure because the linked info sheet was for a "passive buzzer" that is different from the one I have in my hand, image 1. It had other components that are not in the passive buzzer in image 1. It looked more like the one in image 2.
Here is the experimental observation:
I went and looked closer, the one you linked to is not the same as image 1. I think some of the problem here is that there seem to be a variety of things called "Passive Buzzer" and several of them work differently.
I just went and checked the passive buzzer in Image 1. It works with 5Vdc at the centre pin. However, it makes no difference in any observable characteristic if the centre pin is connected to 5Vdc or not. I feel pretty safe in saying it is unused.
Looking at your response, you seem to like the terms
Is there any consensus here on that terminology
Keep the audience in mind, I don't want to tell them things that are wrong. At the same time, I do need to keep the material approachable.
What does the "module" of image 1 has on the other side of the board? If it has no other components, I agree with you that the center pin doesn't have to be connected.
For us to have a consensus, it would be nice to have others opinions. But
this is what I´m calling standalone passive buzzer --> 
and this is one passive buzzer module --> 
It is good to hear that smart kids get good schooling regardless of economic level! Very good!
Perhaps use terms the parts are sold by and make sure the kids learn that? It is so they can order for themselves.
It seems to me that the 3 pin module likely has a transistor that the signal switches or gates (if FET or BJT) so that small power signal controls external power for louder sound.
If you can, teach the kids about non-blocking code. Back in the 80's it was called Main Loop Code and used to write games on 6502 'toy computers'. At the simplest level, beginners can learn this... non-blocking and finite state machine to do button and led with very short code, there are MANY examples that do not have extra details to confuse. I wrote some of them, I try but more explanation can be added. Send me PM if you want any, it is for the kids and the future as they are the future.
I don't know that it will make sense to expose your students to this information, but you should be aware that the buzzers shown in your pictures contain electromagnetic speakers; not piezo discs. When you have a module with a driver, the distinction probably doesn't matter, but there are significant differences between the two if you are using the buzzer component alone.
I mention this because other models of buzzers do contain a piezo disc and piezos have been mentioned throughout this discussion (based on the reasonable assumption that is what you meant by "buzzer" since you hadn't specified). Confusingly, the sellers of these buzzers often describe them as "piezo" in the product listings, but if you crack one open you will find an electromagnetic actuator.
What does the "module" of image 1 has on the other side of the board?
Nothing, just a couple of traces going to the pins on the Passive Buzzer.
There is a trace to the centre, what you considered the Vcc pin, but that trace goes to nothing. It looks like it is there for some other use of the small board.
It really is just a Passive Buzzer on a board with a three-pin header. There are no other components.
I note that piezos are like capacitors. They can absorb current but don't conduct DC. Would you say they need limiting resistors?
(based on the reasonable assumption that is what you meant by "buzzer" since you hadn't specified). Confusingly, the sellers of these buzzers often describe them as "piezo" in the product listings, but if you crack one open you will find an electromagnetic actuator.
This is the core of the confusion, there seem to be a lot of different things called both "buzzer" and "passive buzzer." I was just hoping that it could be cleared up a little so I am not teaching something that will need to be unlearned.
The code from the Arduino looks like this:
tone(BUZZER_PIN, 80, LOOP_DELAY);
One thing I like about using the driven passive buzzer is that it can be turned off. It seems that the LED is introducing quite a bit of hum into the circuit. However, with the driven passive buzzer, I can simply turn it of when it is not in use,
digitalWrite(buzzerVccPin, HIGH); //added to reduce hum
tone(BUZZER_PIN, 80, LOOP_DELAY);
delay(LOOP_DELAY); //added to reduce hum
digitalWrite(buzzerVccPin, LOW);} //added to reduce hum
Understand, this is not a starting point, this is 2/3rds of the way into the class. That said, yes, these sketches are still using delays. Mills gets introduced later.
Here is the basic project hardware:
yes, I know my desk is a mess.
Unfortunately I'm not very knowledgeable in this area. But some of the other forum helpers certainly are so hopefully they will provide an answer.
