Look at the edges of your chess board. You will notice that along one side it says 1,2,3,4,5,6,7,8 and on the other side a,b,c,d,e,f,g,h with this system squares or entire rows can be specified. such as the 1st rank, 2nd rank, 3rd rank, 4th rank, 5th rank, 6th rank, 7th rank, and 8th rank. Files can also be specified, a file, b file, c file, d file, e file, f file, g file, and h file. Squares are referred to by their place in the grid. So if a square is in the e file and on the 4th rank, it is the square e4.