If you want to know what factoring is, then you need to know what factors are. Factors are the operands in a multiplication. If you want to "factor" a number, X, then that means you want find some set of other numbers that yield X when they are all multiplied by one another. Similarly, if you want to factor some algebraic expression, that means you want to find some set of two or more other expressions that can be multiplied together to get the original.