The term 'TYPE OF VACUUM FLASK' can be answered with the word 'DEWAR', which is a five-letter word. A Dewar flask, also known as a vacuum flask, is an insulated container that is designed to keep its contents at a constant temperature. It was invented by Scottish scientist Sir James Dewar in 1892 and is commonly used to store liquids such as liquefied gases, liquid nitrogen, and other cryogenic liquids. The vacuum flask consists of two flasks, placed one inside 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.