Birthday (noun)

1. The day of a person's birth.
2. The anniversary of a birth.

Origin:

Old english bēorthdæg, from bēorth "birth" + dæg "day".

Examples:

1. He was celebrating his birthday.
2. She got a cake for her birthday.
3. His birthday is on July 15th.
4. It was her birthday and she was having a party.
5. I forgot his birthday, can you remind me?