What is "speech balloon"

n. A speech bubble.

Speech balloons (also speech bubbles, dialogue balloons or word balloons) are a graphic convention used most commonly in comic books, comics and cartoons to allow words (and much less often, pictures) to be understood as representing the speech or thoughts of a given character in the comic. There is often a formal distinction between the balloon that indicates thoughts and the one that indicates words spoken aloud: the balloon that conveys subjective thoughts is often referred to as a thought bubble.