Sat means reality. The truth, the actual, opposite of ‘Asat’ - not true, not reality. Very often we look at ‘Asat’ and think that it is ‘Sat.’ What we think is real may not be real. And what we think is not real, because we cannot see it tangibly, may be real. So, ‘Sat’ means Truth without frills and the reality which is the opposite of that which is not real.