Answer:
A vacuum flask (also known as a Dewar flask, Dewar bottle or thermos) is an insulating storage vessel that greatly lengthens the time over which its contents remain hotter or cooler than the flask's surroundings. Invented by Sir James Dewar in 1892, the vacuum flask consists of two flasks, placed one within the other and joined at the neck. The gap between the two flasks is partially evacuated of air, creating a near-vacuum which significantly reduces heat transfer by conduction or convection.

The typical design of a Thermos brand vacuum flask, used for maintaining the temperature of fluids such as coffee.

Laboratory Dewar flask, Deutsches Museum, Munich

Diagram of a vacuum flask

A cryogenic storage dewar of liquid nitrogen, used to supply a cryogenic freezer
Vacuum flasks are used domestically, to keep beverages hot or cold for extended periods of time, and for many purposes in industry.
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