In general, any file format for digital data that does not consist of a sequence of printable characters (text). The term is often used for executable machine code.
A common class of binary files is programs in machine language ("executable files") ready to load into memory and execute. Binary files may also be used to store data output by a program, and intended to be read by that or another program but not by humans. Binary files are more efficient for this purpose because the data (e.g. numerical data) does not need to be converted between the binary form used by the CPU and a printable (ASCII) representation.