OK, I give up. A search for threads that might enlighten me seem to only yield results where everyone apparently knows what it is and doesn't need to spell it out. Digging through the customary online retailers was no help either.
So, I'll bite - who or what is SRD? It's important because it's good stuff and I don't have any of it. Please tell me it doesn't have something to do with a burlap bag and "snipe". :)