All the words on this site are licensed under a Creative Commons Attribution-NonCommercial 4.0 International License. Sweet!
This license means you're welcome to use the content however you see fit, as long as you're not profiting from it ("non-commercial") and as long as you link back here or mention my name ("attribution"). As a matter of politeness, however, it would be nice if you asked permission before republishing any full-length essays. Thanks!
Everything above applies to the text on the site. As to the images — well a lot of them come from other sites, and God only knows what licenses I've broken by copying them here. I try to cite sources whenever I remember (and have the energy to bother), i.e., about half the time (⍨). If my cavalier attitude has led me to mis-use any of your content, please get in touch and I'll try to rectify it ASAP.
My own diagrams, on the other hand — those that have been fashioned in MSPaint or any of its modern equivalents — are available under the license above.