What is a "Community Tank" of fish?

Here's some very good advice from our newest link pal, The Skeptical Aquarist on assembling a true community fish tank.

The results generally don't rise above a harmless menagerie, but they will normally lack any ecological significance. Cichlid tanks especially seem to be assembled on the basis of "Can this new one hold its own?" An increasingly tense mosh pit is added to, one new arrival at a time — "Can I fit one more in?" — until finally mayhem breaks out.