Writer's Fallout Shelter

I've never seen an "unprofessional" designation, but the difference is in pay rate. For instance, a publication that pays $.03 per word is semi-pro whereas one that pays $.05 per word would be a pro. (I'd have to double-check the scale to confirm the cut-off, but I think $.05 per word is the minimum you can pay and be considered a pro market.) In most places I've seen those that pay less than the semi-pro rates designated as either "No Pay" or "For the Love" markets.

The databases and market lists that sort the markets like that are just helping their subscribers pre-sort the markets.