A birthday is an annual event that marks the anniversary of an individual's birth. Humans particularly enjoy celebrating their birthdays as they usually get presents and a birthday party is usually thrown in their honor.
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")