Definition of birthday boy in English:

birthday boy

noun

informal
  • A boy or man whose birthday is being marked.

    • ‘It was in the school hall and the birthday boy was sitting up on stage.’
    • ‘In the smaller house next door, all of three feet away from the farmhouse, the birthday boy's mother and father are staying, along with the birthday boy's niece.’
    • ‘The birthday boy or girl will receive an autographed football with every child receiving goody bags, which will include a voucher to see a City game.’
    • ‘And I'm not sure the fact that you popped out to buy an emergency (and somewhat clichéd) gift will stand you in any stead with the birthday boy.’
    • ‘Everything else - cake, balloons, party bags - has to be provided by the birthday boy's parents.’