What is "liar paradox"

In philosophy and logic, the classical liar paradox or liar's paradox is the statement of a liar who states that they are lying: for instance, declaring that "I am lying" or "everything I say is false". If they are indeed lying, they are telling the truth, which means they are lying. In "this sentence is a lie" the paradox is strengthened in order to make it amenable to more rigorous logical analysis. It is still generally called the "liar paradox" although abstraction is made precisely from the liar themself. Trying to assign to this statement, the strengthened liar, a classical binary truth value leads to a contradiction.

If "this sentence is false" is true, then the sentence is false, but if the sentence states that it is false, and it is false, then it must be true, and so on.