in aviation:

• UHF Direction Finder, a kind of radio direction finding (RDF)
• Unducted fan, a type of jet engine

in informatics:

• Uniqueness Database Files, a Windows XP Professional configuration text file
• Universal Disk Format, an operating-system-independent file system commonly used on DVD and other digital media
• User Defined Field, a user-defined field that can be added to tables in a database
• User Defined Function, an external function which can be called from a PHP or SQL server, such as MySQL or from a dBase type of language.

in politics:

• Ulster Defence Force
• Union Defence Force
• Union of Democratic Forces, a political party
• Union pour la Démocratie Française, a centrist French political party
• United Democratic Forces, an electoral alliance in Bulgaria
• United Democratic Front, a political party
• United Democratic Front (South Africa), a former anti-Apartheid movement in South Africa

other:

• Ultra deep field, a view of the distant universe taken in 2004 by the Hubble space telescope
• United Dairy Farmers, an American chain of ice cream shops.
• Up Side Down Suspension Forks, used in Motorcycles and Mountain bikes