birthday birthday /ˈbɝːθˌdeɪ/

noun

1. () An anniversary of the day on which a person was born (or the celebration of it)  ( birthday )
   an anniversary of the day on which a person was born (or the celebration of it)
    I am planning a surprise birthday party for my best friend next week
   I am planning a surprise birthday party for my best friend next week
   
   
2. () The date on which a person was born  ( natal day , birthday )
   the date on which a person was born