hedge lecture

Noun. Also a verb, "hedge-lecturing". An unofficial and often illegal peer-to-peer educational method, done totally outside the purview of the educational establishment, in which one person teaches another some technical skill which can potentially be misused for harmful purposes. It is derived from "hedge sermon", when early Protestant clerics were banned by the Vatican from preaching in Catholic churches.

1. Vera gave me a hedge lecture in chemistry in her dining room. 2. I'm hedge-lecturing Max about how engines work.