noun
The anniversary of the day on which a person was born, or the celebration of that day.
今日は私の誕生日です。
Today is my birthday.
友達の誕生日にプレゼントをあげた。
I gave a present to my friend for their birthday.
生年月日 is the full date of birth (year, month, day), often used on official forms, while 誕生日 refers to the birthday celebration or the day itself.
Compound of 誕生 (birth) and 日 (day). The reading たんじょうび is a standard on'yomi combination.