Initialism of open-source software
"The technician installed several new operating systems on the server to improve performance."
Alternative form of 'oss
plural of OS
In plain English: An OSS is an organization that runs secret spy missions for a government.
"The old building is made entirely of stone and brick, with no glass oss visible in its walls."
Initialism of Office of Strategic Services (a United States intelligence agency formed during World War II)
"Before it became the CIA, the OSS was the primary US intelligence agency operating during World War II."
The origin of the word oss is unclear, though it likely stems from Middle English ōssen, which originally meant "to reveal" or "to prophesy." This verb may be a variant of an older form related to Old English hālsian, although that earlier term carried different meanings such as "to beseech" or "to exorcise."