What does the term 'professional' artist** really mean and how should it be measured?  

Should it be measured by percentage of income? or time spent? 

Should it be measured by quality of artwork? (How? Who's quality?)

Does or should 'good practice' come into it? 

Do the terms 'voluntary' artist and 'community' artist suggest a lack of seriousness and professionalism?

Does it depend on the artist's intended career path? 

**By 'artist' please read as a wide remit! It could be interesting to compare different artforms and their own benchmarks...