What does the idiom pop quiz mean?

A "pop quiz" is an unannounced quiz given to students in a class. It's called a "pop quiz" because it appears suddenly and unexpectedly, like a "pop" or a burst.

Here's why it's called a "pop quiz":

* Surprise: The "pop" in "pop quiz" refers to the element of surprise. It's unexpected and catches students off guard.

* Suddenness: The quiz "pops" into the class like a surprise. It's not something students are prepared for in advance.

Essentially, a pop quiz is a quick assessment that teachers use to test students' understanding of the material they've been learning.