Although everybody already described it pretty well, I thought this might be handy
. Here is an excerpt from the Red Dwarf FAQ
What does "smeg" mean?
It's a word made up by Grant Naylor for the characters to use as an all-purpose profanity. Some fans have theorised that it was derived from smegma (a particularly unpleasant bodily secretion), but Rob and Doug deny this. In the interview on the CD included with the Six of the Best box set, they state that "we wanted to invent a futuristic curse word which had the right sort of consonant and vowel arrangement to make it sound like a genuine . . . curse word." In an online chat session, Doug Naylor said "I think it's Latin for clean, also there's an Italian washing machine company [<http://www.smeg.it>] called Smeg. Also each of the letters S-M-E-G stand for smelting metal and something to do with the washing machine process." A detailed list of "smeg" references in the show is available at <http://www.bristol.u-net.com/smegweb/docs/smeglist.html>
Berry, Patrick M. Red Dwarf Frequently Asked Questions List (FAQ). <http://home.interpath.net/pat/rd/faq.html#Smeg>