A weak/tight player is one who:

a) is a calling station (plays weakly) until he/she has a hand.
b) will tend to bet only with made hands/the nuts.

Case in point--the classic:

You hold QQ

Flop 8-9-3 rainbow. You lead, WT opponent calls.
Turn 4 completing rainbow. You lead, WT opponent calls.
River J. You lead, WT opponent raises, you call, opponent shows QT for the rivered straight.

Best way to play a weak/tight player is to semi-bluff and bluff more, but valuebet a lot less. And never call his raises without something close to the nuts.