Tautology is useless restatement, or saying the same thing twice using different words. “Speedy sprint" is a tautology because sprint already means "speedy running."
The noun tautology originates from the Greek word tautologos, meaning “repeating what is said.” "A pedestrian traveling on foot" is a tautology because a pedestrian, by definition, is someone who walks. In the study of logic, a tautology is a statement that is necessarily true under any interpretation and cannot be denied without introducing logical inconsistencies. "It will snow tomorrow, or it will not snow tomorrow" is an example. No argument here — it's true any way you look at it.