What is a cable stop?
 

What is a cable stop, and is there a site where I can input certain bike terms and get an answer? Google did not work. tia

Cable stop:
http://www.sheldonbrown.com/gloss_ca-g.html#cablestop

I always go to Sheldon Brown's site when I have a question..
http://www.sheldonbrown.com/glossary-c.html

Cable stops are points on the bike where the cable housing goes in one end and the bare cable (inner wire) comes out the other end (without the housing).

Sheldon has a nice glossary for most bike-related terms:
http://www.sheldonbrown.com/

And the next question will be: Why use them? The cable housing is not needed for straight runs of control cables, as the frame can serve it's purpose. Eliminating the housing where possible saves weight and reduces friction in the controls.

Weight savings is not enough to really be worried about. Often times the housing is eliminated where unnecessary. If it isn't, there probably is a reason, such as aerodynamics.

just built a new pugsley with full housing...and tell ya...new top quality housing is pretty friction free nowadays

Unnecessary housing can also make brakes feel "mushy" since housing will compress whereas a solidly mounted cable stop will not.

nokon style housing eliminates any and all mush

Yeah, but they're expensive and (IMO) ugly.

true dat