Google says no one on the web has used the term 'misfenestration.'
So I shall, and I shall define it, too:
'Misfenestration' is when you type into the wrong chat window by accident. In Second Life, if you type local chat like "No, that's not a cucumber!" into the group chat for, oh, say, SL Hobos, your misfenestration will be mocked.