Shared library loaded by C and C++ programs when they start; contains functions and other shared program logic; used for loading common libraries into memory so multiple programs can use the same codebase even though they run in separate operating system processes.

Shared libraries can be created from .O files, which contain compiled C or C++ code. SO files are typically saved to designated places in the file system and then linked to by programs that require their functions. SO files are commonly built with the "gcc" C/C++ compiler that is part of the GNU Compiler Collection (GCC).