Triceratops means "three-horn face". It was a plant-eating dinosaur that lived towards the end of dinosaur times (68 -65 million years ago) and so lived at the same time as T-rex, and may even have been its food. Triceratops belongs to the group of dinosaurs called ceratopsids.
It is very distinctive because it had a frill of horn. This may have been used in the same way as reindeer now use their horns.