A cornstarch and water mixture used in thickening stews, sauces, etc. The term has been used by U.S. Army mess hall cooks, and it is presumably derived from its resemblance to bull semen.
A polite way to dismiss or reject something without having to say bullshit. Typically used by parents, teachers, adventurous clergy, and youth guidance counselors.
(...in AP Bio class for example)
Teacher: "And so the mitochondria...blah blah blah etc"
Confused student: (smashes face on desk) "Ahhh what is this bullfuckery. It makes no sense >.<"
or something such as...
(rainbow unicorn flies across the sky and eats rainbows and poops butterflies and brings you cookies)
Person: wow...bullfuckery...wtf just happened...win...
or perhaps...
Student A: "oh crap, i forgot to do my homework"
Student B: "way to go"
Student A: "yeah...ill just write down some bullfuckery"