The function strcmp is a standard library function in the C programming language used to compare two strings. It takes two string arguments and returns an integer value based on their comparison. If the strings are identical, it returns 0; if the first string is lexicographically less than the second, it returns a negative value; and if the first string is greater, it returns a positive value. strcmp is case-sensitive, meaning that uppercase and lowercase letters are treated as different characters. This function is commonly used in various applications, such as sorting strings or checking for equality in user input. Understanding how to use strcmp is essential for effective string manipulation in C programming.