The Collaborative International Dictionary of English v.0.48:

defenestration \de*fen`es*tra"tion\
   (d[-e]*f[e^]n`[e^]s*tr[=a]"sh[u^]n), n.
   the act of throwing (something or someone) out of a window.
   [PJC]

WordNet (r) 3.0 (2006):

defenestration
    n 1: the act of throwing someone or something out of a window

The Jargon File (version 4.4.7, 29 Dec 2003):

defenestration
 n.

    [mythically from a traditional Bohemian assassination method, via SF
    fandom]

    1. Proper karmic retribution for an incorrigible punster. ?Oh, ghod, that
    was awful!? ?Quick! Defenestrate him!?

    2. The act of completely removing Micro$oft Windows from a PC in favor of a
    better OS (typically Linux).

    3. The act of discarding something under the assumption that it will
    improve matters. ?I don't have any disk space left.? ?Well, why don't you
    defenestrate that 100 megs worth of old core dumps??

    4. Under a GUI, the act of dragging something out of a window (onto the
    screen). ?Next, defenestrate the MugWump icon.?

    5. [obs.] The act of exiting a window system in order to get better
    response time from a full-screen program. This comes from the dictionary
    meaning of defenestrate, which is to throw something out a window.