Here is a link to The Cook's Thesaurus - Beef Loin Cuts
Scroll to the bottom and there is a picture of a Tri-Tip....although the ones we get are much thicker. We also get ours already trimmed so there isn't as much fat as in the picture. We have never had a problem with tri-tip being tough...but I think the marinading helps...and not over-cooking it. :-)
Discover the Great Taste of Beef Tri-Tip
This flavorful beef cut has been one of the beef industry's best kept secrets. Tri-tip was seldom marketed when carcass beef or beef quarters were delivered to retail markets because there are only two tri-tips per carcass. This meant that there was not enough for a case display. Consequently, the butcher would grind or cube it. Today, most stores receive boneless boxed beef. If you don't see tri-tip in the meat case, ASK FOR IT. It may be temporarily out of stock. Tri-tip roasts can be ordered separately if your butcher knows there is a demand.
A beef tri-tip roast is a boneless cut of meat from the bottom sirloin. It also is called "triangular" roast because of its shape.
(Sheesh!....I can't imagine someone grinding up a perfectly good tri-tip! LOL)
More info and recipes : Discover Beef Tri-Tip