A birthday was the anniversary of a person's birth, and the event occurred once a year. Human birthdays were sometimes marked with a birthday party, which could include giving the birthday person a present.
Every year, Elizabeth Singh would light candles and pay homage to her children, Rahel and Esthappen, who were assimilated by the Borg at the Battle of Wolf 359. (Star Trek: The Cantabrian Expeditions: "Devil's Cube")
In 2373, three days before his birthday, USS Cantabrian Captain Noah Wrightson sacrificed himself to stop Samantha Delaney's temporal weapon from firing on Earth. (Star Trek: The Cantabrian Expeditions: "By All Means Necessary")