Once you mix all your tracks down to a 2-track (left & right) stereo mix, anything that you do with that stereo mix (additional efx, mastering, EQing, etc) would be considered mastering. It's like fine-tuning your 2-track mix into a final mix.
In most cases, the better it was mixed down from multi-track, the less "fixing" you will assumedly do during mastering.
STRATEGY