2: A celebration commemorating such a date.
n: the date on which an event occurred in some previous month (or the celebration of it)
In dumb down stupid terms: A monthly anniversary, though usually only used in context for the first 12 months
Committing to an offical relationship by mutual choice, and celebrated on the first month after the date that you asked one another to be your partner.
Boy: Will you be my girl friend
(one month later)
Girl: i got you something for our Montaversary.
Boy: Oh yeah. . . Thats so sweet. . . What is it?
Girl: Its a surprise
Boy: I got you something too~
(After exchanging gifts, on your Monthaversary, you are committed to one another.)
2. Celebrating the day of something by months
Cassidy: "Oh! its april 5th! its also my monthaversary!"
Stephanie: "Oh thats cool. How long have y'all been dating now?"
Cassidy: "23 months!!!"