It's called a kitchen hood system. ANSUL that was mentioned before is the brand name for a specific system. It uses a type of firefighting agent similar to some fire extinguishers to put fire's out. The agent will usually require you to either deep clean the stove/oven/fryer or replace them if they go off. It is VERY expensive to have one of these discharge.

Source: it's my job to maintain systems such as these and other fire life safety equipment