DEFINITION OF LEVEL TERMS
COMMUNITY (AVERAGE): A player who is able to keep up, but has some trouble in all areas of playing (rhythm, key signatures, intonation, tone, tempo, technique, range, musicianship), has some difficulty applying direction, but has a good attitude, works hard and will work for free or doesn't require much in the way of payment for services.
COMMUNITY (ADVANCED): A player who has a good command of the instrument(s), but still has minimal problems in a couple of areas (rhythm, tempo, intonation, musicianship), can take direction, has a good attitude, works diligently at the part until acceptable (or better), and while still not requiring much in the way of pay, deserves some monetary compensation for the time and effort, if not mileage.
PROFESSIONAL: A person who is very good to exceptional in all areas of performance, requires very little direction, but expects, will take and apply direction, can sit in at a moments notice and sound as though the part has been rehearsed. This person may or may not be a member of the American Federation of Musicians (or Actors Equity Union), generally requires substantial compensation for his time, knowledge and training, but will negotiate.
UNION QUAILITY: Any musician who has no perceivable problems in any area of performing, but is willing to perform with persons of lesser ability than him/herself (provided that they are at least striving for and obtain a minimum level of excellence). Takes direction well and applies that direction without having to be reminded. Is NOT currently a member of the American Federation of Musicians (or Actors Equity Union). Requires, for the most part, union-level compensation, but will negotiate.
UNION: Any person who is a current member of the American Federation of Musicians (or Actors Equity Union), who will only be hired by a union contractor (or equity house), and will only perform with other members of the union at union-scale payment under a contract.
NOTE: These are my own personal definitions! They do not necessarily mean that the person(s) to which they are applied are absolutely rigid in their stand or 100% fit the definition into which they have been categorized. Depending on the peronality of the individual, the personality of the person hiring him, and the situation for the gig, you may find that the boundaries for certain definitions tend to blur, or overlap.