Tautology
Etymology
From Greek "tauto," "the same," a contraction of "to auto," plus "logos," "word" or "saying." The literal sense is "saying the same." In logic the term narrowed to mean a formula true under every interpretation, but in ordinary use it flags the deflating discovery that a grand-sounding claim reduces to A is A.
noun · /taw-TOL-uh-jee/
A statement that is true by definition and therefore conveys no real information, saying the same thing twice in different words.
What it names
The empty sentence that sounds like an argument — "it is what it is," "the rules are the rules" — where the conclusion just restates the premise and no ground is actually covered.
Example
Defining a good leader as someone who leads well is a tautology, not a definition.
Related idea
A tautology fails by saying too little; a truism is true and informative in principle but so obvious that repeating it adds nothing.