1.
aim, purpose, goal
What one is aiming for or trying to achieve. Often used to describe the real objective behind an action.
2.
attraction, draw
The main thing one wants to see, get, or experience. Used with お to form お目当て.
Usage
Sense 1 often appears in the pattern ~目当てで (for the purpose of ~) or ~が目当て (one's aim is ~). Can carry a negative nuance when describing ulterior motives: 金目当て (after money).
Sense 2 uses the polite prefix お: お目当て (the thing one is looking for). Common in shopping and tourism contexts.