Have you got the Theory of Poker ebook? it's by Sklansky.

Have a search for the word 'expectation' and you'll see examples of Expected Value dotted throughout the book. It's basically whether or not a particular play would be profitable if it were repeated a large number of times. If it's profitable, then it's positive expected value (+EV).

Check out the section on bluffing for Fold Equity. It's essentially the chances that your opponent will fold if you bet. The higher your FE, the higher the chance they will fold to a bet.

/nutshell