[Sal Giaco]

For what it's worth, this is how I distinguish between the two:

The AMLU are Professional Umpires that work Affiliated Minor League Professional Baseball. They are guys that are considered "in the game". They are Professional Umpires because that is their career.

SCump, myself, etc are amateur umpires that work Independent (Minor League) Professional Baseball. We are NOT considered as being "in the game" and we work these leagues mainly as an advocation (hobby) rather than a career.

I think there's a difference between working pro ball and being a Professional Umpire. We are amateur umpires that work professional baseball - the AMLU are Professional Umpires that work Minor League baseball.

This goes back to why I said people need to be careful how they list their experience. As an unwritten courtesy to MiLB umpires, I never reference my summer work as Minor League baseball - I simply term it as Independent Pro Ball.