Derivative of the word ‘fucking’, 'effing' means litterally ‘F-ing’. You may see it used on a message board where derogatory words (such as the f-word) are not allowed, to take the place the un-allowed.(Note that on sites such as GameFAQs, this is known as censor bypassing, and you most likely will get modded for it, whether be by a nobleman or some n00b merely&purely because s\he can.) It is, however, its own, unique word, seperate from ‘fucking’ or ‘f'ing’ or ‘F-ing’ in its entireity.
The reason that "I'm late for class"'s definition of this word has received such low ratings is for the fact that s\he acted as a ‘language elitist’ and instantly put the word down, when in actuality s\he did not know the etymological origin of the word and whe\how\under what contexts.. it is generally used.