A library is a file that contains data referenced by an application. It may contain functions, classes, constants, variables, and other types of data that are used by one or more programs.

Libraries are often accessed using a linker, which is a function that loads data from a library into the program. While generic libraries may have a ".lib" extension, dynamic libraries typically have a .DLL extension (Windows) or a .DYLIB extension (Mac). Static libraries often have a .A file extension.