It's a backronym from pinyin, Wikipedia says:

> BYD is the pinyin initials of the company's Chinese name Biyadi. The company was originally known as Yadi Electronics (亚迪电子), named after the Yadi Road in Dapeng New District, where the company was once based.[24] According to Wang Chuanfu, when the company was registered, the character "Bi" (比) was added to the name to prevent duplication, and to provide the company with an alphabetical advantage in trade shows.[25] As the name "BYD" had no particular meaning, BYD started adopting a backronymic slogan "Build Your Dreams" when it participated at the 2008 North American International Auto Show in the US.[26][27][28]