Open and closed guard are self explanatory. One you have your ankles crossed, one you don't.
Spider guard - feet in their biceps, grips on your wrist.
TK guard - open guard with feet overhooking your opponent's calves or ankles.
X-guard - underhooking a leg so their ankle is next to your shoulder, with one foot placed behind their knee and the other by their waist.
De La Riva guard - an open guard variation where you control a sleeve and hook around the back of the knee on the opposite side of their body.
Octopus guard - In full guard, sit up to one side so your armpit is next to their hip, grip around their waist and keep your head close to their hip.
Upside down guard - as I understand it, imagine your are on the bottom of a north/south position facing upwards with your face in their belly but with your feet in their biceps or armpits and controlling their wrists, almost like a spider guard variation.
Rubber guard - with one leg around the small of their back, bring your other leg up their back so you can secure a Gable grip around your ankle, which should be behind their neck.
Roleta guard - as I understand it, basically you are facing your opponents feet with their biceps behind the creases of your knees with your butt against their chest.
What else do you need to know? BTW, people feel free to correct me. Stephan Kesting has a pinball guard that he uses but I can't even begin to try explain it.