The same as everyone else's. You're in over your head if you have to ask what the meanings of basic terms are. If you read my post, you will find an identity that will lead you to a definition.
Dude, I think you are in over YOUR head!
Tautology From Wikipedia, the free encyclopedia.
In logic, a tautology is a statement that is true by its own definition. All true statements of logic are tautologies.
Outside logic, it sometimes means a useless tautology, that is, one that is uninformative (or in colloquial terms, stating the obvious). This definition is imprecise, as all statements are informative in some context.
In traditional grammar, a tautology is a redundancy due to superfluous qualification, often leading to the schoolboy definition of "saying the same thing twice".