Tautology, like you said is a way of expressing something by repeating or saying it in a different way or different ways. This can be used for emphasis, to convey something important, or to add beauty to a text. However, many times its use is inadvertent and is just a needless repetition.
A logical statement which is neither a tautology nor a contradiction is a contingency.
A tautology can be verified by constructing a truth tree for its negation: if all of the leaf nodes of such truth tree end in X's, then the original (pre-negated) formula is a tautology.''