The song "Do They Know It's Christmas?" was written in 1984 by Bob Geldof and Midge Ure to raise money for famine relief in Ethiopia. It was performed by Band Aid, a supergroup of British and Irish musicians, and released in December 1984. The song quickly became a Christmas number one hit in the UK and other countries, raising millions for charity. The title phrase "Do They Know It's Christmas?" implies a concern about whether people suffering in famine-stricken areas are aware of the Christmas holiday, highlighting the contrast between the plenty enjoyed by some and the hardship faced by others. The lyrics express a plea and awareness of global disparity during Christmas time. Over the years, the song has been re-recorded and re-released to raise funds for various humanitarian causes related to famine and crises in Africa. Despite some criticism about its portrayal of Africa, the song remains an iconic charity anthem closely associated with Christmas and charitable giving.

So in short, "Do They Know It's Christmas?" is a famous charity song that asks if people suffering from hardship know it is Christmas, using the holiday as a symbol to raise awareness and funds to help them.