SDI

SDI is a three-letter abbreviation with many expansions. It's impossible to count exactly how many expansions it has, but it's surely one of candidates for the first place.

• Single Document Interface
• Strategic Defense Initiative
• Szybki Dostep do Internetu[?], later renamed to Staly Dostep do Internetu[?]

Less common expansions include:

• Saratoga Direct Inc.
• Sarawak Development Institute
• Schaumburg Dienstleistung für Informationstechnik
• Scientific Development and Integration
• Scuba Diving International
• Selective Dissemination of Information
• Serial Data Interface
• Service Dimensions Inc.
• Seoul Development Institute
• Socratic Dialogue Inducing Lab
• Software Dynamics, Incorporated
• Southern Dental Industries Limited
• Soluzioni d'Impresa
• Spatial Development Initiatives
• Space Science and Engineering Center (SSEC) Desktop Ingestor
• Spatial Data Infrastructure
• Spatial Data Integrations, Inc.
• Stamp Dealers International
• State Disability Insurance
• Statistics on Depository Institutions
• Steel Deck Institute
• Steel Dynamics Inc.
• Strategic Diagnostics Inc.
• Strategic Directions International
• Strengthening Democratic Institutions Project
• Sustainable Development Indicators
• Sustainable Development Information
• Sustainable Development Initiative
• Systems by Design of Illinois
• Systems Documentation, Inc.