1. A long narrow opening; a crack or cleft.

2. The process of splitting or separating; division.

3. A separation into subgroups or factions; a schism.

4. Anatomy A normal groove or furrow, as in the liver or brain, that divides an organ into lobes or parts.

5. Medicine A break in the skin, usually where it joins a mucous membrane, producing a cracklike sore or ulcer.