tech rep is short for Tech Support Representative or Technical Support Representative.

Techs, for shorter, are a larger population though are of the same breed.

Tech Reps are usuaully designed/created to solve problems, as opposed to a Sales Rep, who is bred to exploit problems.

Tech Reps usually drink tasty caffeinated beverages, while sales reps drink spring water and fruit juice.

Tech Reps keep to themselves, while sales guys want to be everyones friend.
.... when a Sales guy is around, the tech often keeps a tight hold of his wallet.