in terms of dating and relationships I would think it means that you know the layout of the male/female dynamics and what the opposite sex wants. You what to do and when to do it. Basically you are a master at the dating scene.
omg if you don't know what tis means you need help when people say you have game that means that you know how to attract the opposite sex ur confident, not corny, usually this applies to guys not irls that's y you hear guys saying I spit game
If you have game, it means you're attractive to others and can easily get a girl/boyfriend.