To very much over simplify: Some problem are "easy", there is a way to solve even complex ones with a (relatively) small amount of effort. These are P. Other

To very much over simplify: Some problem are "easy", there is a way to solve even complex ones with a (relatively) small amount of effort. These are P. Other problems have no known "easy" method and the solution to a given problem can only be determined by something like brute force, such as trying every possibility.