A segmentation fault is an error that occurs when a program tries to access a memory location that it is not allowed to access. This can happen if the program attempts to read or write to an area of memory that has not been allocated to it, or if it tries to access memory in a way that is not permitted. When a segmentation fault occurs, the operating system typically terminates the program to prevent it from causing further issues. Developers often use debugging tools to identify the source of the fault, which can help them fix the underlying problem in the code.