Probability is the what that something will or will not occur?

Probability is the likelihood that something will occur. If you subtract it from 1, we get the likelihood (or probability) that it will not occur.

If a coin is tossed and rolls heads 6 times, the (empirical) probability of obtaining a head is 6/10 or .6.

1-.6 =.4 is the empirical probability (or likelihood) of not getting a head.