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.
Often, a formal distinction is made between the balloon that indicates thoughts and the one that indicates words spoken aloud; the balloon that conveys thoughts is often referred to as a thought bubble or conversation cloud.
The most common is the speech bubble. It is used in two forms for two circumstances: an in-panel character and an off-panel character. An in-panel character (one who is fully or mostly visible in the panel of the strip of comic that the reader is viewing) uses a bubble with a pointer, called a tail, directed towards the speaker.