Definition: Not in the OED, perhaps surprisingly. Presumably the position one assumes while pooping. A Wallace-ism?
Other: See, for example, “I can picture deLint and White sitting with their elbows on their knees in the defecatory posture of all athletes at rest...” (Infinite Jest, pg. 9)
SNOOT score: 1 (both because it’s a Wallace-ism and because it’s hard to be SNOOTy about poop)