can someone tell me what it is

 

when combustion occurs, the air squeezes past the piston rings, which gives you horrible compression and you lose mad power.

 

During combustion some of the high presure gasses leak past the piston rings. That is blow-by. A little is normal, it can't be completely be eliminated. If you think you have too much blow-by, it can be verified with a leak-down test.