The two-letter abbreviation BI has several different meanings:

• BI is the ISO country code (ISO 3166-1 alpha-2) for Burundi.
• .bi is therefore the Internet top-level domain for Burundi.
• the IATA code for Royal Brunei Airlines
• "bi" is also a prefix for two, such as bicycle, binoculars, or bilingual
• "Bi" is also common internet slang for "bye"