A vest or jacket worn like a garment and giving buoyancy. To earn
its name it must be designed in such a way that the wearer naturally floats on
his back, with mouth and nose held up clear of the water. A distinction is made
between a lifejacket proper, and various kinds of buoyant waistcoats and vests
giving lesser degrees of buoyancy (but greater freedom of movement). It all
depends on the type of boating you do. In the USA the generic term is PFD
(Personal Flotation Device). Several grades of PFD are approved by the US Coast
Guard, for differing circumstances.