Wiktionary
n. A life vest or other device or article of clothing designed to be used by one person as an aid to remaining safely afloat in water, especially in a emergency situation.
Wikipedia
A personal flotation device (abbreviated as PFD; also referred to as a life jacket, life preserver, life belt, Mae West, life vest, life saver, cork jacket, buoyancy aid or flotation suit) is a piece of equipment designed to assist a wearer to keep afloat in water. The wearer may be either conscious or unconscious.
PFDs are available in different sizes to accommodate variations in body weight. Designs differ depending on wearing convenience and level of protection.
Usage examples of "personal flotation device".
We know he had a personal flotation device, and he was hale and hearty enough to think about saving someone's skin other than his own.
The tiny personal flotation device was no thicker than a bicycle inner tube.
She hit the release on her Personal Flotation Device, called a Mae West by all and sundry, and rolled up to the surface of the water.