A number of any length, but often either 6, 8, or 32 characters long, that is calculated from a much larger data block (typically a frame, file, or image) in a way that is sensitive to any change in the original data.The checksum is calculated by the sender and either appended to the data block or delivered separately, as are MD5 checksums for software files.The receiver independently calculates a checksum and compares the two values as a means of detecting errors created in transit, or perhaps deliberate alterations of the data.The term cyclic applies to the calculation method, which is binary long division of the original data by a derived number until there is only a remainder, which is the checksum. See also checksum and cyclic redundancy check.