An abbreviation of the word 'FRIENDS' or 'FRIENDS FOREVER' from 'Best Friends Forever' or 'Bff.' Typically used between two Bff's who have created nicknames for each other from 'BFF,' one friend is Bee and the other is Eff Eff (or just Eff for short.)
Spellings of this word Eff can range from, 'Eff to Effffffff' depending on how many f's you prefer. Further nicknames include, Effaroo, Effness, Effy, Eff Eff Effness and EffLochness.
Mary: Hey bee
Jen: Hey Eff
Mary: Bee i'm in such a hmmf
Jen: Don't worry we'll be bee's and eff's forever.