tautology

Short definition from Wiktionary

Noun

1. 1
   Redundant use of words, a pleonasm, an unnecessary and tedious repetition.
2. 2
   An expression that features tautology.
3. 3
   A statement that is true for all truth values of its propositional variables.
4. 4
   A statement that is true for all truth values of its Boolean atoms.