A standard C function that appends a copy of the source string to the destination string.
The declaration of strcat function which is found in string.h is:
char *strcat(char *dest, const char *src)
This function appends the string pointed to by src to the end of the string pointed to by dest. Here,dest is a pointer to the destination array, which should contain a C string, and be large enough to contain the concatenated resulting string and src is the string to be appended. This should not overlap destination.
strcat returns a pointer to the resulting string dest.
For more information, check the man page.