Taylor's pretty good about not acting like she's singing if she isn't. She does use backing tracks a lot but she's able to maintain her voice because her songs just aren't challenging at all vocally and she writes within her range.
The backtrack is just very very loud. It looks more like she letting the backtrack kinda substitute for her vocals so she can focus more on the adlibs or whatnot
re·verb
ˈrēˌvərb,riˈvərb
noun
an effect whereby the sound produced by an amplifier or an amplified musical instrument is made to reverberate slightly.
a device for producing reverb on an amplified musical instrument.
plural noun: reverbs