A vacuum flask, also known as a thermos, is a container designed to keep liquids hot or cold for extended periods. It consists of two walls with a vacuum in between, which minimizes heat transfer through conduction and convection. This design helps maintain the temperature of beverages like coffee, tea, or soup. Typically made from glass or stainless steel, vacuum flasks come in various sizes and shapes. They are commonly used for outdoor activities, travel, and everyday use, making them a popular choice for people who want to enjoy their drinks at the desired temperature, whether at home or on the go.