Floating Production, Storage & Offloading vessel. Usually out of service tankers are utilised as FPSO's. Found on http://ports.co.za/maritime-terms.php
Floating Production Storage and Offloading vessel - a floating facility installed above or close to an offshore oil and gas field to receive; process; store and export hydrocarbons.
Found on http://www.contractorsunlimited.co.uk/glossary.shtml
(PROJECT GLOSSARY) Floating Production, Storage and Offloading vessel - Term for a type of oil 'rig' used in the offshore oil & gas industry. Found on https://www.encyclo.co.uk/local/20479