1. [from X-Men comics; originally “bampf”] interj. Notional sound made by a person or object teleporting in or out of the hearer's vicinity. Often used in virtual reality (esp. MUD) electronic fora when a character wishes to make a dramatic entrance or exit.
2. The sound of magical transformation, used in virtual reality fora like MUDs.
3. In MUD circles, “bamf” is also used to refer to the act by which a MUD server sends a special notification to the MUD client to switch its connection to another server (“I'll set up the old site to just bamf people over to our new location.”).
4. Used by MUDders on occasion in a more general sense related to sense 3, to refer to directing someone to another location or resource (“A user was asking about some technobabble so I bamfed them to http://www.catb.org/~esr/jargon/”.)