A control character is a non-printable character in a computer system that does not represent a written symbol but instead performs a specific function. These characters are used in data streams to control how text is processed, formatted, or transmitted. Examples include characters that signal the start or end of a text block, or those that instruct a printer to move to a new line. Control characters are part of the ASCII (American Standard Code for Information Interchange) and Unicode character sets. They play a crucial role in communication protocols, such as HTTP and TCP/IP, ensuring that data is correctly interpreted and displayed by devices and software.