Every few months, I find it necessary for some reason, to describe something about how the various W3C roles/terms work together at a high level. It takes about 400 words and, rather than continue to type them over and over, I thought I'd simply create a linkable thing that I can just point to instead. Hooray for links!
The W3C itself is really designed to allow various interests to work together and have some kind of way to help reach large group concensus toward open standards. Most of the work that happens in the W3C happens under the banners of in either Community Groups or Working Groups. Both of these formats are, primarily, designed to facillitate discussion in a way less encumbered by potential intellecutual property and patent issues. The former is more wide open and the latter the more formal step on the way to standardization with more necessary rigor.
Fundamentally, the way this is accomplished and the way the consortuim is held together involves what is called the Advisory Committee (AC). When an organization joins the W3C, they must name an AC representative. The AC Representative then is in charge of, as the name suggests, representing their organization in helping 'run' the W3C. What this means, in practice, is that AC Representatives are, for example, the ones who say "I release this person from my organization to particpate in such and such group, attend meetings, and work 'in the open' on standardizing what is in the charter". The AC Representatives also are in charge of ulitimately making decision about how the W3C itself works.
Two groups within the W3C though are different: The Technical Architecture Group (TAG) and the Advisory Board (AB). The TAG is in charge of looking across all the work and keeping the "vision" of all of the work being done at the W3C healthy, coherent and working synergistically to remain healhty in the very long term (think 50-100 years). In some ways, you can kind of think of it as a steering committee for work and focus. The Advisory Board (AB) is in charge of advising the Advisory Committee on any changes that have been suggested to the way the W3C operates, answer questions, etc - before it is ultimately voted on by the AC.
Each of these groups are a very small number of people nominated and chosen by the AC members themselves to hold these roles by election to serve for two years.