What is time(NULL) in C?

Question

I learning about some basic C functions and have encountered time(NULL) in some manuals.

What exactly does this mean?

Answer 1

int main (void)
{   
    //print time in seconds from 1 Jan 1970 using c   
    float n = time(NULL);   
    printf("%.2f\n" , n);      
}      

this prints 1481986944.00 (at this moment).