tank raised suggests that the clown is raised in a fish tank, acclimated to tank life and will usually be accepting of prepared foods.
Wild caught (the regular ones) are just the opposite. Wild clowns are not used to living in a fish tank, and will often accept prepared foods, but this is foreign to them. Often times wildcaught clowns will harbor parasites.
One thing to look for in clowns is aquacultured clownfish. These are farm raised (captive raised and captive bred) and are very hardy fish
frank