Definition of ‘Topside’
The upper part of an oil platform—above the water line—that holds the drilling rig, oil production plant and accommodation block (lodging). On an FPSO or on a boat, topside refers to the hull area between the water line and the deck.
Investopedia explains ‘Topside’
Topsides are often designed to be modular. Their components can be rearranged and replaced as needed. Oil platforms are expensive, and modular topsides lower the costs and reduce the difficulty of technological upgrades.