The function malloc (memory allocation) is used in the C programming language to dynamically allocate a specified amount of memory during the execution of a program. It returns a pointer to the beginning of the allocated memory block, which can be used to store data. If the allocation fails, it returns a null pointer. When using malloc, it is important to free the allocated memory using the free function to prevent memory leaks. The size of the memory block requested is specified in bytes, and the programmer must ensure that the requested size is appropriate for the data being stored.