Not a dumb question.
Lots of websites give confusing/wrong information.
Piezo: passive piezoelectrical device that can be used as vibration sensor (microphone) or to make sound (speaker).
Buzzer: A 'thing' that makes a 'buzzing' sound (can be anything electrical or mechanical).
Some 'buzzers' are passive (you have to provide a tone), some are active (tone generator buildin).
One way to test if a buzzer is active or passive is to connect a DC voltage (5volt) to it.
If it makes a tone, it's active, and you can't use it as as a speaker (for custom tones/sound).
So "piezo buzzer" tells me that it's made of a piezo element and can make sound.
But it doesn't tell me if it's active or passive.
Leo..