is the repetitive use of phrases or words that have similar meanings, essentially saying the same thing twice.

My favorite is “Act now and get a free gift!”

“Really! I usually pay for gifts.”

How about ‘advance planning?'

That's much more effective than after-the-fact planning, don't you think?

Free gifts and advanced planning are tautologies—straight from the department of redundancies department!

While sometimes seen as a fault of style, can be used deliberately for emphasis or clarity.

Saying ‘The results are completely and utterly fantastic' uses to strengthen the sentiment expressed.

But be cautious with tautologies. Use them intentionally and cleverly or they'll clutter your message and make it less effective.