A checksum is a small piece of data derived from a larger set of data, used to verify the integrity of that data. It is created by applying a mathematical algorithm to the original data, producing a unique string of characters. When the data is transferred or stored, the checksum can be recalculated and compared to the original to ensure that no errors occurred during the process. Checksums are commonly used in computer networking and data storage to detect errors. For example, when downloading a file, a checksum can confirm that the file has not been corrupted. If the checksums match, the data is likely intact; if not, it may need to be resent or repaired.