Mild hybrid, full hybrid & PHEV

A mild hybrid (MHEV) has a small electric system, usually 48 volt, that supports the combustion engine when pulling away and recovers braking energy. The car cannot drive purely electrically, or barely; the gain is a modest reduction in consumption, in practice roughly a few percent depending on use.

A full hybrid (HEV, also self-charging hybrid) has a larger electric motor and battery and can drive short stretches, especially in town, fully electrically. It charges itself via the engine and braking energy and has no plug. The gain is largest in urban traffic and smallest on the motorway.

A plug-in hybrid (PHEV) has a considerably larger battery and a charging connection, with an electric range that depending on the model is typically a few tens of kilometres WLTP. Actual consumption depends heavily on how often it is charged: driving almost always electrically and short gives low consumption, charging rarely and a lot of motorway gives consumption that approaches an ordinary petrol car. See utility factor for how that assumption sits in the WLTP statement.