Other forms: mementos; mementoes
A memento is a keepsake of something you want to remember. You may keep photographs as a memento of a great family reunion — except for that one photo where Aunt Bonnie is wearing the lampshade and singing "Respect." No one wants to remember that!
Memento is a Latin imperative that ordered people to "Remember!" People love to keep mementos from all sorts of things, including weddings, births, concerts, trips, holidays, and even school. You should be careful not to bore people with your mementos, however. Not everyone wants to see the ribbon you wore in your hair at the homecoming game, and your 8,000 pictures of your trip to Paris (Illinois, not the one in France) might be a bit over the top.