Loctite calls this goop 30534 liquid thread sealant with PTFE/Teflon. The sheer amount of oxygen required to say that could keep several people alive for a month, so I’ll take a page from Smitty’s book (the oldest mechanic I ever worked with) and call it “pipe dope.”
Essentially, PTFE thread sealant is an improved, liquid (but very viscous) version of Teflon tape with a few noteworthy advantages. It’s not direction-sensitive, so the new guy won’t wrap pipe threads backwards, and it provides a better seal thanks to its anaerobic hardening properties (much like regular Loctite). You don’t need to keep different thicknesses around for different pipe thread sizes, either. The only major disadvantage is that Teflon tape has no set time, whereas this needs to be left alone for a few hours before use. This can be inconvenient, since an awful lot of repairs are done on pipe threads.
If you can let the assembly sit for a while, a $5-$7 can is a good idea. I’ve found it’s much more reliable than Teflon tape and does a very good job making up for pipe threads’ shortcomings. Larger hardware stores and industrial supply houses are your best bet if you’re trying to lay hands on a bottle, but if that chair’s just too comfortable, there’s always the Internet.
Loctite PTFE Pipe Thread Sealant [Google Products]