A birthday is the date when someone is born, however in the context of the indieweb, it is a feature displayed on some silos' user profiles that you can (or must) enter, and some prominently present to your friends on the month and day of your birthday, like Facebook's "BIRTHDAYS THIS WEEK" feature at the top of their events page.
- Ashton McAllan on http://acegiak.net/ using
dt-bdayin her h-card on her home page since (????-??-??)
- Aaron Parecki publishes the month and day of his birthday using
dt-bdayon his home page h-card since 2016-02
Facebook has had a birthday field in user profiles since pretty close to the beginning, including separate privacy levels for the date (day & month) and year:
with various privacy levels for the "Year":
Year dropdown privacy menu options:
- My Followers
- People I Follow
- We follow each other
- Only me
On your birthday, when people visit your profile page, balloons fly up from the bottom of the screen:
IndieWebCamp sessions about birthdays:
Birthdays are often used as part of a person's identity and thus publishing a precise accurate birthday pose an identity theft security risk. As a result, people at some IndieWebCamps have self-reported as using non-real birthdays on silos.
Birthdays are often used by social networks to create spurious notifications - see Friendster's line in this video