No. As kh54s10 pointed out you can use a bag with any method of brewing that uses grains, however the term BIAB or "brew in a bag" in common use generally refers to the ALL GRAIN method of using a bag rather than a mash tun.
The 3 brewing methods are:
1) Extract: + or minus steeping grains which usually are held in a bag
2) Partial mash: part of fermentables come from a mash, part from extract. Many do use a bag because they are convenient for small mashes but some people use a mash tun
3) All grain: all your fermentables come from grain. You can do this with a mash tun or BIAB method
