Here is the definition from allrecipes.com:
This Scottish specialty is made by stuffing a sheep's (or other animal's) stomach lining with a minced mixture of the animal's organs (heart, liver, lungs, and so on), onion, SUET, oatmeal and seasoni ... MORE
Tripe is the lining of the stomach, and the heart, liver, and kidneys are giblets. My mother, brother, and sister were all from Glasgow, so I wasn't mincing (pardon the pun) words.
I think a Robert Burns dinner is one of the few places haggis is served now, thank the Lord!