Just to clarify what WDWKat stated...Equity covers those who are mic-ed while performing a "character"(this is why Cindy in Cinderellabration is equity, but when you meet her in the park or watch parade, she is not.) or who are following a script (Jamie in Playhouse Disney, the host in Millionaire etc) Equity also covers singers and dancers, such as those in FOLK and B&B. Their contracts are for a year, and they have to negotiate their contract when it expires each year.
People who dance in the parades, and now in some shows (like Cinderellabration) are not Equity but are in the character Dept (which is covered by Teamsters..yes the same union as bus drivers...go figure) The difference there is technical...character performers arent allowed to do kicks above the waist (although it does happen), do double turns, or lifts over head. there are exceptions to the rule and there are many other things that separate characters from Equity, but that's just the tip of the iceburg.
WHEW!