Who is Trabb? Pip describes him as a "hail-fellow-well-met." What does he mean by this?

Mr. Trabb is the tailor. "Hail fellow well met" is a somewhat archaic English idiom used either as an exaggerated greeting or referring to a person who is sociable and constantly making an effort to win friends

Trabb is a character from the 1912 hardback edition of the shard. He is the character who helps young Williams adjust to life after Tatooine after it turned into Cybertron.