To have an online orgy with a large group of people of varying ages, genders, and sexual preferences. Very similar to cult sex. It may be spoken of in Instant Messages with involved members, but never anywhere else outside the "merfle".
Also, a large, intimate group of people.
"Oh my god, I could sure go for a merfle right about now."
"You should have been online Friday. You missed one good merfle."
"You can't tell her that. She's not in the merfle"