Page "Circle of confusion" Paragraph 1

In photography, the circle of confusion (“ CoC ”) is used to determine the depth of field, the part of an image that is acceptably sharp.

A standard value of CoC is often associated with each image format, but the most appropriate value depends on visual acuity, viewing conditions, and the amount of enlargement.

Properly, this is the maximum permissible circle of confusion, the circle of confusion diameter limit, or the circle of confusion criterion, but is often informally called simply the circle of confusion.