What is a file descriptor?

A file descriptor is an abstract indicator used to access files or other input/output (I/O) resources in operating systems. It's typically a non-negative integer managed by the operating system and used by programs to identify and manipulate files or I/O streams. File descriptors can represent various types of resources, including files, pipes, sockets, and devices. They serve as a bridge between user-level applications and the operating system's I/O subsystem, enabling operations such as reading, writing, and manipulating file positions.