Definition of nutsé
When we say that a player is nutsé, it is because his range is composed mainly of extremely strong hands. When we say a player is nutsé when he pushes all in preflop, we mean that he regularly pushes all in with AA and maybe sometimes with KK. The strength of his range is at its maximum. This is useful information to have when making hero folds. If you have a king color on the river, you are betting and your opponent pushes all in with a "nutsé" row, it's probably a good time to fold.
Identifying nutsés rows with your HUD
To identify the nutsés ranges of his opponents, nothing better than a tracker with a HUD. Thus, we can evaluate the frequencies of our opponents to extrapolate their range. For example, you make a 3bet preflop and a player you 4bet. In your HUD, you look at his % of 4bet and you see that he 4bet nutsé% of the time. That's huge. Here, your opponent is not necessarily nutsé. But if the same player 4bet 0.5% of the time, he is nutsé. 0.5% of the time is the mathematical frequency at which you will receive a pair of aces preflop. The chances of it being nutsé are huge!