Generally it means 5 1/4" back from the LE of the wing at the root chord. Or think of it this way: draw a line down the middle of the bottom of the fuselage lenthwise from the motor to the tail, then measure 5 1/4" back from the LE of the wing. That's the starting CG point, and you'll probably end up adjusting it to personal taste 1/4" either way.