Whee, an off-the-rails discussion on semantics! I'm in!
So here's the low down:
Speaking in an EE context, what is known as "buzzers" can only make one specific tone. They are driven by an internal oscillator, you only need to apply a set voltage. They "buzz" on their own.
"Speakers" (colloquially also "beepers" or "tweeters") can make any sound, their oscillation is driven by an external circuit. (x86 has always done this using PWM, and will always do this, if only to be able to make two sounds that differ in tone height.)
Whether it is piezo or magnetic driven is not relevant in this context, although one tends to speak of "beepers" for piezo speakers because they lend themselves much more to single beeps.
"Beeper" would be the best choice, if only to stay consistent with kmod-gpio-beeper. Also not every "beeper" is a "buzzer", but every "buzzer" is a "beeper." And "speaker" should remain reserved to proper loudspeakers.
[Edit: Paragraph removed due to unavailability of the "sarcasm" font, no doubt an error in the forum's stylesheets.]