Calling function is a function which is declared within main function. Called function is a function which sends result after processing the code to the calling function in main function.
For ex...
main()
{
int a,b,c;
a=5;
b=8;
c=add(a,b)
printf(c);
}
int add(int y, int x)
{
int z=y+x;
return z;
}
here c=add(a,b) is a calling funtion and add(y,x) is a called function.