Can anyone define what is a thermos flask in brief ?? Plz!!!

Dear student A thermos flux is a thermally insulated container that is used to hot water or other liquid like tea, milk etc., so, that the liquid remains hot for a longer time. The space between the inner and the outer wall of the flux is vacuum. Thus, heat cannot be conducted from the surrounding into the flux. So, hot liquid remains hot and cold liquid remains cold within a thermos flux. Regards