Military

• Iceland Defense Force
  Iceland Defense Force
  The Iceland Defense Force was a military command of the United States armed forces from 1951 to 2006. The IDF, created at the request of NATO, came into existence when the United States signed an agreement to provide for the defense of Iceland, which does not, and did not, have its own unified...
  
  
• Irish Defence Forces
• Israel Defense Forces
  Israel Defense Forces
  The Israel Defense Forces , commonly known in Israel by the Hebrew acronym Tzahal , are the military forces of the State of Israel. They consist of the ground forces, air force and navy. It is the sole military wing of the Israeli security forces, and has no civilian jurisdiction within Israel...
  
  
• AIDC F-CK-1 Ching-kuo, a light fighter aircraft
  Air superiority fighter
  An air superiority fighter is a type of fighter aircraft intended to gain air superiority in a war, by entering and seizing control of enemy airspace. Air superiority fighters are designed to effectively engage enemy fighters, more than other types of aircraft...
  
   created for the Republic of China Air Force
  Republic of China Air Force
  The Republic of China Air Force is the aviation branch of the Republic of China Armed Forces. The ROCAF's primary mission is the defense of the airspace over and around Taiwan...
  
   under its Indigenous Defence Fighter program
• Identify, Insured Deposit Fund

Non-military

• Île-de-France
  Île-de-France (région)
  Île-de-France is the wealthiest and most populated of the twenty-two administrative regions of France, composed mostly of the Paris metropolitan area....
  
  , a region of France
• Intel Developer Forum
  Intel Developer Forum
  Intel Developer Forum , is a gathering of technologists to discuss Intel products and products based around Intel products. The first IDF was in 1997...
  
  
• Intermediate distribution frame
  Intermediate distribution frame
  Intermediate distribution frame : In a central office or customer premises, a frame that cross-connects the user cable media to individual user line circuits and may serve as a distribution point for multipair cables from the main distribution frame or combined distribution frame to individual...
  
  , a cable rack for telecommunications wiring
• International Diabetes Federation
  International Diabetes Federation
  The International Diabetes Federation is a worldwide alliance of some 200 diabetes associations in more than 160 countries, who have come together to enhance the lives of people with diabetes everywhere. For over 50 years, IDF has been at the vanguard of global diabetes advocacy...
  
  
• Integrate Data Facts, a market research company
• Inverse Document Frequency, a factor in the tf–idf
  Tf–idf
  The tf–idf weight is a weight often used in information retrieval and text mining. This weight is a statistical measure used to evaluate how important a word is to a document in a collection or corpus...
  
   principle
• International DOI Foundation, the developer of Digital object identifier
• Intensity-Duration-Frequency curves.