What is "equity"?

I have seen in many videos that pro players often mention the "equity" of their hands. Now, according to what I understand, it is the expected value of that hand. So, a couple of aces would have an equity of 80% preflop? In that case, professional players know the "equity" of all the hands of their rank, and how does it change with the flop cards?

Equity in poker is the share of the pot that is yours based on the odds that you will win the pot at that point in play. Equity changes after each street – pre-flop, flop, turn and river.
cardchat can help you - https://www.cardschat.com/poker-equity.php

Equity is the chance, that a given hand will be the best hand at showdown. It can be calculated for a single hand as well as a range on hands. There are many different programs, that can do it. In real time you dont know your exact equity, because you dont know your opponent(s) hand(s), nor their exact ranges. But you can estimate it and have an idea about, where you stand.

It is weird that it is the objective of the game and at the same time it is something that no one defines when they are explaining to you how to play the game.

here is a simple calculator insert any hands and see the equity of your hand, there is still flopzilla, and much more, everything will come with time, the main thing is to play!
https://www.pokernews.com/poker-tools/poker-odds-calculator.htm

I had some trouble to swallow the meaning of this word in poker language, because it is very different of its true meaning in formal uses. But I have heard some meanings that are closer from dictionary.

1. When your call in a final pot is no more than your odds. When your odds are 33%, you should not to call more than 33% of final pot.
Ex:
Pot 1000 chips
Odds 33%

You should not to call more than 1000 chips, because the first pot has 1000 chips, villain bets 1000, so you call with 33% (1000 chips) of a final pot (3000 chips). When you pay more than that, your call becomes negative in the long run.