TM - short for Tokyo Marui, manufacturer of high quality (and price) airsoft weaponry (among other things) http://en.wikipedia.org/wiki/Tokyo_Marui
WE - another manufacturer of airsoft weaponry. Quite a name in the gas blowback market but making significant inroads in the electric market too http://www.weairsoft.com/
DMR - Designated Marksman Rifle basically the weapon of a soldier fulfilling a role partway between sniper and infantryman http://en.wikipedia.org/wiki/Designated_marksman_rifle
"they take 100% TM parts" - Tokyo Marui were the first to design a number of parts for airsoft (the hop up unit for example) so many other manufacturers have copied them This means that many airsoft weapons being based on Tokyo Marui designs will take Tokyo Marui parts which can be better than the manufacturers parts as the copies are usually produced to a lower cost. Often a phrase applied to sniper rifles based on the Tokyo Marui VSR10.