In many FTP client programs, a command that instructs the FTP client to display a pound sign (#) each time it sends or receives a block of data.
— Computer ScienceA fixed-size result that is obtained by applying a one-way mathematical function (sometimes called a hash algorithm) to an arbitrary amount of data. If there is a change in the input data, the hash changes. The hash can be used in many operations, including authentication and digital signing.
— Computer Science