Assuming genuine curiosity, I'll bite. I think most people refer to "Shit Law" as being small (<20, more likely 2-10 attorneys per "firm") and low paying ($40k-60K/year). They typically practice under the guise of "general practice", which could mean tickets, misdemeanors, wills and trusts, real estate, or whatever they can find. The pay is substantially less than BigLaw and the work is much less prestigious. There are worse case scenarios, and the work isn't entirely uninteresting - just not particularly well respected.
ETA: 0L here, didn't realize the forum. Do have experience in the area though.
Also assuming genuine curiosity, the pay is generally lower at least at the beginning stages of your career. But I never understand why someone would consider it not well respected. Doing work for fortune 500= respect; doing work for individuals=no respect? Being originally from a small town, I always felt small law was where all lawyers worked. it's classic real lawyering. It was only later I even knew what biglaw was.
(someone with experience in small law environment on both client and law firm side)
Edit: most lawyers in this country do not work for big law firms
It's a byproduct of the changes in law over the past generation. The real income of solo attorneys has gone down 30% over the last generation, from $65k (adjusted for inflation) to $45k. At the same time, tuition has exploded. Consider the lawyers you have encountered in your small town. The ones that are in the middle of their career (~45 y/o) graduated in the early 1990s. At the time, you could get a law degree from the University of Michigan for $22,000 in tuition (in-state), or about $33,000 in today's dollars. Tuition today for the same degree is about $140,000 (in-state). Even at a third-tier in-state school it will be close to $90,000 (in-state).
So back in 1992, when you graduated from a local school with maybe $25,000 in debt and went to go to work for a small firm for $35,000, life wasn't so bad. Yeah, the folks who went to Cravath were making $80,000, but your own personal situation was reasonable. In 2012, most people will graduate from a local school with $100,000 in debt, and will be making $45,000 at a small firm. That's where the "shit" part comes in.
We get it. Things are so much harder now and it's not fair.
Edit: not everyone is taking out ridiculous loans. There are ways to get around those tuition hikes...scholarships, etc.