The term 'anorak' refers to a heavy, hooded jacket usually in the form of a pullover long enough to cover the hips.
The invention of the anorak is credited to the Inuit people of Greenland, who used the word "annoraaq" to refer to their outdoor garment of choice.
Anorak.com calls its namesake a "fashion mainstay of the socially inept," and refers prospective anorak buyers to the Berghaus, Gap, Marmot, and Patagonia websites. I can vouch for the last two manufacturers, as well as Columbia and The North Face as being excellent manufacturers of all-weather outerwear.
Anorakcorner.com claims that the term's derogatory use stems from 1960s fuck-the-BBC pirate radio enthusiasts, who would wear their hooded jackets on boat trips out to see the actual pirate radio ships broadcasting from the North Sea.
It has since become British slang to refer to anyone with a fanatical devotion to any topic as an 'anorak.'
(This would most likely cover a good portion of e2.)