Explanation:
A file descriptor is an integer handle or reference used by an operating system to access files or I/O resources like sockets and pipes. When a process opens a file, the operating system assigns a file descriptor to track interactions with that file.

In UNIX and UNIX-like operating systems, file descriptors 0, 1, and 2 are reserved for standard input (stdin), standard output (stdout), and standard error (stderr), respectively. File descriptors simplify resource management by abstracting hardware-level details from applications.

Developers use system calls such as open(), read(), and close() to manipulate files using file descriptors. These descriptors are essential for managing concurrent access to files and network resources.

Formal Definition:
A file descriptor is an integer reference assigned by the operating system to identify and manage open files and I/O resources within a process.

Additional Information:
File descriptors are often implemented as entries in a process-specific file table maintained by the operating system. This table maps descriptors to file locations, access permissions, and buffer states.

Efficient file descriptor management is crucial for handling multiple open files without resource leaks. System limits often restrict the maximum number of file descriptors a process can hold at a time.