Generally, a checksum is a unique number string that is derived by running an algorithm against a specific set of data. Once a checksum is generated it allows an easy comparison between two sets of data that are supposed to be identical. The checksums will be identical if (and only if) both sets of data are identical. The current “industry standard” algorithm is MD5. A checksum is sometimes called a hash.
A checksum tool (there are many) can generate and compare checksums. As a confidence check, users can generate a checksum for a file and provide it along with the data via file copy, download, or other means of delivery. When the data is received at the destination the accompanying checksum can be compared against a checksum generated from the copied data. A checksum is routinely provided with software downloads and other data. In Post Production, final masters are often delivered with a checksum, to help ensure that media content is delivered without error.