What are the word and thought bubbles in cartoon strips called?

The bubbles used in comic strips to denote thought or talking are called world bubbles, speech bubbles or word balloons. These bubbles are so named because of their shape, which often resemble balloons.

Word balloons are used by comic strip writers to portray a variety of emotions and speech and include a tail that denotes which comic book character is doing the thinking or talking. The bubbles have been used in almost all comic book incarnations, although comic book writers try to limit the number in an effort to not clutter the page with text and block the graphics too much.