No part. Chickens come from chickens, not cows.
Loin
The head
Angus beef does not come from any part of any cow, but comes from a BREED of cattle (or cows) called Angus.
http://ask.metafilter.com/27259/How-much-meat-is-there-on-a-cow
The part of the cow that fajita meat comes from is the plate. Traditionally, fajita meat is made from skirt steaks which is made from the plate of the cow.
The upper part of the cow.
They come from where you might think, the head of the cow on either side, attached to the cheekbones.
The hind quarter, in front of the round.
The part of a cow that shredded beef comes from is the chuck roast. Shredded beef is also known as ground beef.
Tenderloins are from the loin area which is on the side of the back.
http://ask.metafilter.com/27259/How-much-meat-is-there-on-a-cow