TENS (Unit)	:=	The 'Transcutaneous Electrical Nerve Stimulation' unit is used by chiropractors to cause involuntary muscle contraction. Sadomasochists use it for fun rather than therapy. (see also Electro Stimulation)
Top	:=	A dominant male or female person - the person in charge/control (also Dom, Domme). Opposite: Bottom.
TPE	:=	Total Power Exchange - term for an extreme form of a 24/7 D/s relationship (see also TPE)
Transsexual	:=	Person in the process of physically changing sexes
Transvestite	:=	see Crossdresser
TT, (Tit Torture)	:=	Intense breast stimulation (for example with needles, clamps, tight bondage etc.)
Trainer	:=	A trainer is one who teaches the sub/slave "new tricks" - don't mix this up with the term Master/Mistress

For a brief discussion of the terms Master, Trainer, Protector and Mentor please checkout Master John's Explanations - Thank's to mj for pointing us towards this resource.