This article is from the rec.heraldry FAQ, by Gordon Findlay (email@example.com) and Francois Velde (firstname.lastname@example.org) with numerous contributions by others.
The SCA (Society for Creative Anachronism) is an international
living-history society which researches and recreates many elements of
medieval life, from battles to feasts. It has an active group of
heralds, kings-of-arms and so on, who exercise considerable influence
over the heraldry used in the SCA's activities.
There are other such groups, but the SCA is by far the largest.
Many SCA heralds participate in rec.heraldry, but please keep
SCA-specific discussion in more appropriate fora (see question 2).