A foam is a solution of gas in a solid or a liquid.  An example of foam would be a sponge.  The froth on the surface of mug of soapy water is also foam.  In a foam, bubbles of gas are separated by a solid or a liquid medium. 

Foams can be open celled, in which the gas can enter or leave the foam or close celled, such as bubble wrap, where the gas is trapped and cannot move. 

Foams find application in fire extinction.  Many fire extinction methods use foams, particularly for fires caused by oils and other flammable materials.  Mattresses and cushions are also examples of foams. 

Foams are used for thermal insulation and for shock protection.