Wiktionary
n. A large structure used to house workers and machinery needed to drill and then produce oil and natural gas in the ocean.
Wikipedia
Oil platform P-51 off the Brazilian coast is a semi-submersible platform.
]] An oil platform, offshore platform, or (colloquially and incorrectly) oil rig is a large structure with facilities to drill wells (optionally), to extract and process oil and natural gas, or to temporarily store product until it can be brought to shore for refining and marketing. In many cases, the platform contains facilities to house the workforce as well.
Depending on the circumstances, the platform may be fixed to the ocean floor, may consist of an artificial island, or may float. Remote subsea wells may also be connected to a platform by flow lines and by umbilical connections. These sub-sea solutions may consist of one or more subsea wells, or of one or more manifold centres for multiple wells.