The standard library in C programming refers to a collection of built-in functions and header files that are part of the C programming language. These functions and header files are specified by the C Standard, which defines the syntax and semantics of the C programming language.

The standard library provides a wide range of functionality that can be used in C programs, including input/output operations, string manipulation, memory management, mathematical functions, and more. Some of the most commonly used header files in the standard library include:

• stdio.h: provides functions for input/output operations, such as reading from and writing to files, the console, or other devices.
• string.h: provides functions for manipulating strings, such as copying, concatenating, or comparing strings.
• math.h: provides mathematical functions, such as trigonometric functions, logarithmic functions, and more.
• stdlib.h: provides functions for memory management, such as dynamic memory allocation, sorting, searching, and more.

To use the functions and data types provided by the standard library, the corresponding header file needs to be included in the C program using the #include preprocessor directive. The standard library functions can be called like any other function in C programming, by passing arguments and returning values as necessary.