A callout is an explanation in a specific area of an example or image that helps explain what it's describing using an arrow, line, or number. A callout is often used in publishing, such as books, manuals, technical specifications, and other technical materials.
Example of a callout
In this case, it points to a line of code and offers additional details. A callout could also be used for other purposes, such as labeling parts of a machine in an image.
How is a callout created?
A callout in an image, like the one shown above, can be created in any image editor that creates arrows, circles, lines, numbers, and text in an image.