We can all see split ends when they happen but do you actually know what they are and what causes them? Split ends (or trichoptilosis, to get fancy and scientific) occur when the cuticle, the protective outer layer of each hair strand, gets stripped away and the dry, vulnerable hair underneath splits. Although there are lots of "split-end mending" products out there, fixing them actually isn't possible, so once you've got 'em, you've got to cut them off.
The only way to avoid split ends is to prevent them. This means deep conditioning, not over-coloring your hair, and minimizing your use of heated styling tools (flat irons, blow dryers, curlers, etc.). If you're going to color and style constantly regardless, you can still help safeguard your hair by using a treatment that structurally reinforces it, like Nexxus Emergencee Strengthening Polymeric Reconstructor ($15), which can help stop splits from spreading and prevent new ones, and by getting your hair trimmed regularly.
Photo by Flickr user Kimberly Robyn