OOP is a simply an acronym that stands for out of position . Being out of position  means to act first on each betting round. Being out of position is considered to be a disadvantage since the out of position player does not get to see what his opponent does before acting on each street.

The spots or marks on the face of a card. When used as a verb, the term refers to a card beating another by a single pip   i.e., outranking another by one.