Look refers to the maximum number of algorithms that you have to use to orient the last layer.
If you just learn the beginner method, then I think that is a 3 or 4 look OLL. If you learn about 9 algorithms for the OLL, then you can always orient the last layer using just 2 of them. If you learn all of the OLL cases (around 50, I think), then it can always be done in just ONE move.
OLL is the situation where you are getting all the same color pieces on the top. After that you have PLL - permutate last layer, in which you get the pieces into the right positions.