A thermostat is a regulating device, a temperature-activated switch, sensing a physical system's temperature and act for atemperature stays near a point, often drawn as a normally open (NO) (to open a circuit) or normally closed (NC) (to close a circuit) contact responding to temperature changes.
A thermostat symbol is often drawn as a switch symbol labeled (e.g., "TH" or "TSTAT") with a temperature-sensitive activation.
NO (Normally Open) thermostat closes if temperature reaches a set point.
NC (Normally Closed) thermostat opens if temperature exceeds a set point.
the symbol of a normally open pressure switch closing at a set pressure.
[1] Wikipedia