I use it in different ways.
It can be a goal, as in "master your forms". Sort of like "perfection". It's a goal, and anyone with humility knows that it's never achieved - and often is subjective. But we must march to somewhere, and "to perfection" or "to mastery" is as good a goal or endpoint as any. Unfortunately, many declare themselves as having reached "mastery" or "perfection", and that is arrogant.
Lay people have no idea the distinction, often referring to new black belts as "master", and seeing "masterful performances". On one hand, we can correct these people on proper term (at the very high risk of coming across as "arrogant"). Or we can use the phrase in the same manner they use it and find some way to convey that there are better phrases to use - this is where tact and diplomacy plays a role.
But, "master" also has other meaning, even though the user doesn't intend to mean "perfection".
I see "a master" as one who is "an expert" - with more to learn, of course.
I see "to master" as a means "to strive for perfection".
I see "Master" as one who holds a title bestowed either formally by an organization or by well-intentioned lay people.
Few people ever mean "master" to be "omnipotent" or "perfect", as it would in the Bible. And so I don't go crazy when people use it.
I will use it for effect/emphasis/hyperbole: "Go home and master your first form". What I'm meaning to say, is to go home and practice, practice, practice until you know the form inside and out.
I will use it for effect for adjectives: "She performed her form masterfully" or "She mastered her form during her test", (or less formally: "She owned her form").
Then again, in formal education and many professions, a master is one who teaches: "master chef", "headmaster", "master plumber", "master mechanic", "master carpenter". Also, it has titles, even in martial context: page->squire->master/knight, apprentice->master.
So I don't really complain too much when people use it, I tend to know what they mean when they do. But when they cross the line, like "I've mastered this martial art, now I want to do something else", I'll correct them.
Master is a rather overloaded term.
I sometimes like to have fun with the boys, and refer to them as "Master" - as in "Master John, please come here". That is because in English title, a master becomes a mister when he marries. The boys don't really get this, and so they have fun with it for awhile. I don't do this often, mostly for effect. But it shows again that the title is rather overloaded.
EDIT - I know... I rambled... I'll work on that. Sorry..