To cover, surround, or line with a material that slows or stops the passage of heat or cold. In animals insulation would include body fat, fur, feathers, etc.
To protect a room from sound or heat usually by the use of an insulating material such as fibreglass or by creating a thermal or sound break in the construction. This can be done by having two layers of studs slightly offset in a row with the internal lining fixed to one and the external lining fixed to the other. This will stop any direct transference of sound vibration and also help stop direct transference of heat. Creating a gap or space between internal and external surfaces using air as the insulator.