OST

OST can have more than one meaning:

OST stands for Original Soundtrack. The term can be used to describe the musical soundtrack sold for any movie or TV series.
OST is short for the Office of Science and Technology, a British government agency.
'OST' is also the abbreviation and mark of the Taiwan Ostor Corporation, who commonly make Alumunium Electrolytic Capacitors (http://www.ost.com.tw).
'OST' Oostende-Brugge International Airport (IATA Airport Code OST)
Organisation Socialiste des Travailleurs, the Socialist Workers Organisation in Senegal.
OST refers to the enzyme oligosaccharyltransferase.
.OST is a Microsoft Windows file type associated with Micorosft Outlook; part of the Microsoft Office product suite. This file is generated by the application for the purpose of storing the content of the user's mailbox on the local hard drive for offline use. In Office XP and earlier versions, the OST file will become corrupt if its size grows to over 2 gigabytes, generally causing Outlook to freeze up in use or while starting up. Reducing the size of the mailbox and manually deleting the file is the solution for this condition (a new file is created automatically the next time the program is started). Office 2003 features a new format for the file with support for a 20 gigabyte working file size.
Outer Space Treaty

Ost is milk as a firm form. A word in swedish that is.