the date on which an event occurred in some previous year (or the celebration of it). i have heard people talk about their 6 month "anniversary" of moving into a new house, acquiring a car (these folks are typically the ones who anthropomorphize their vehicles with a name, usually something very olde worlde like "beatrice" or "harriet"), or even the 48 hour anniversary of a couple's first sneeze. as upright and walking homo sapiens, with the opposable thumb thing going on, we seem to take much note of anniversaries (note: men are often noted, not taking note, by their female counterparts).
anniversaries are typically defined in relation to a presence or absence; "last time i was with (not with)" or "doing (not doing)" that can either induce kitten and puppy like "awwwww" moments, or the sense that your internal organs have just been removed via a dull melon baller making you want to kill a kitten or puppy. sometimes it's all you can do to get past that repeat of the first time "first", to create space and distance from the not so great anniversaries.
anyway, back to examples.
obviously, there are some associations that will always be embedded. my own are imprinted with a 'ding-a-ling and salivate' unmitigated simplicity; greyhounds (bus, not dog), fluff (baby blanket, not belly button) are synonymous with moi. however, memorial day weekend 2007 is almost upon us and for me it triggers a long out of town weekend, along with 93% of the population of america's trailer parks.
some things we forget with time, age or just not having the environmental cue from the calendar or whevever else. dementia really is something of a double edged sword; while you can remember all the remote "anniversaries", you are unable to recall where you put your teeth to wear to the special occasion.