A word made out of the misspelling of the Swedish term "Fredagsmys".
Fredagsmus can be translated into Fridaypussy or a weekend
vagina.
It's when a woman gets fresh and
clean, preferebly waxed, downstairs, because it's Friday and she wants to party and hook up with some hot dude.
If the woman dances to much, and get all
sweaty she could destroy her fredagsmus (Fridaypussy) and get a discomuff (discopussy) instead.