Arduino and C++ Vocab

Hi. This is nothing too important but I just had a couple terms that I would like to include into my codes but I do not know how to and exactly what they do. Thanks!

analog/ analog pin
else if
const long
unsigned long

threshold - the value at which something changes
analog/ analog pin - I suggest that you look in the Arduino reference
else if - a standard C construct for testing something else after an initial if
const long - a signed long integer whose value will not change
unsigned long - an unsigned long integer whose value may change
interval - the time between 2 events

Thank you!