Liquid smoke is a substance produced from smoke passed through water. Liquid smoke is used for both food preservation and flavouring. During production carcinogens can be removed from the smoke, which can make "smoking" with smoke condensates significantly safer than traditional smoking.
A flavoring, which is in liquid form, made with hickory smoke concentrate, which gives a smoky flavor to foods. The flavoring is very concentrated so it should be used in very small amounts. It can be found in the barbecue sauce section of most supermarkets.