[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.