Gap Concept

[lihar]

here is a link to the video that explains it properly :

http://www.youtube.com/watch?v=VhGf_DBtTGA

THE GAP CONCEPT:
It states that you need a better hand to call a raise with then if you were making the raise yourself. An example is that you are in middle position (one of the middle players to act) and you have KQ suited. If someone raises before you, you should throw this hand away, because someone has shown strength and you need a stronger hand than normal to compensate for this. If the raiser is loose, you can lower your standards. If the raiser is tighter than normal, you'll need to raise your standards for that position dramatically.