EV?

Expected Value.

I hear people talking about it all the time, but never understood it.

How do you figure it out? Like the whole process of getting it.
Is there an article somewhere?

I searched it in the search thing. But didn't find anything. And sorry if theirs an article on the other thread posted about this. The Good tip for beginners one. I didn't read it, just jumped to this.

EV is basically what poker is all about. If you continue to make +EV throughout your poker career youll win, while making -EV plays will cost you money.
For example someone goes all in when you have a flush draw on the flop and you calculate your pot odds and find out that you dont have correct odds to call. If you do call youve made a -EV play and even if you win you will lose in the long run.
Calculating EV is a very difficult process that has many different variables.
Basically in the last post about the good tip hes saying that if you think that a play will only be a slight +EV you should just fold it as theres a big chance a beginner will be wrong and it will actually be a -EV play and even if its not your only getting a small profit out of it.

So, making a mathematically wrong play, will always be -EV right?

Yes but theres also other ways to get -EV.
For examples you have a read on this opponent that he doesnt like to bluff alot.
If you can only beat a bluff and theres is $10 in the pot at the river and he bets $10 your getting 2 to 1 odds to call but have a low chance to win because hes probably betting for value therefore have a - EV and shouldnt call.
Another example would be playing at a normal table calling a raise, reraise, then all in raise with a JJ is almost always a -EV play.

So, making a mathematically wrong play, will always be -EV right?

depends on what you call a mathemically wrong play.

Lets say on the turn the pot is 100, villian bet 40 into the pot, you have a flush draw ~18% to hit. but you assume that if you hit then 50% of the time you will destack the villian of his remaining 500.

Pot odds wise you need to put 40 into a 140 pot 40/140=.28 > .18
so from a str8 pot odds approach you should not call.

but your expected value is .82*0 + .09*140 + .09*540 = 61.2 so you should call