What does answer bubble mean?

In the context of standardized testing, an answer bubble is a small circle or oval on a multiple-choice answer sheet that corresponds to a possible answer for a question.

To mark an answer, the test-taker fills in the answer bubble completely with a dark pencil or pen. The answer bubbles are designed to be machine-readable, so that the answer sheets can be quickly and accurately scored by a computer.

Answer bubbles are commonly used on standardized tests such as the SAT, ACT, and AP exams.