As this is the urban dictionary, I suppose the best definition would be 'sticking something up your arse'! More specifically and for those of a more 'technically minded' nature, it is the use of suppositories or pessaries (hence killing at least one myth, that the 'pessary' is a small bird that lives in New Zealand!..that's a cassowary).
a demonic cult led by the king, bill nye. he has gained a following in the common world from his popular demonic spell courses that are disguised as “online science videos.” science rules all in this cult and the periodic table is used as a ouija board.
billtanists reside on a cold island in an unknown location on earth. they are nocturnal, so they chant texts from the billble all night and sleep during the day.
BILL! BILL! BILL! BILL! BILL NYE THE DEMONIC CULT LEADER!