Docs: Documentation changes, such as YARD markup, or README.md, or something along those lines.
External: touches something in /external, or the Gemfile, or something like that.
Heartbleed: Has to do with heartbleed. This will go away soon, but there are three outstanding still...
Library: Touches something in /lib.
Meterpreter: Has to do with Meterpreter, or depends on a Meterpreter change to land to work.
Misc: plugins and scripts, anything that's not otherwise defined.
Module: Touches something in /modules
Specs: Has specs (an rspec test).
Newbie Friendly: Something that's pretty easy to test or tackle.