Difference between Thermal relief valve and safety valve?

A thermal relief valve is a liquid-only relief due to expansion of a liquid with increased temperature.

A safety valve relieves pressure due to a gas.

It should be noted that "safety valve" is a general term which could refer to Pressure Relief Valves (PRVs) or Pressure Safety Valves (PSVs), terms which are used synonymously in some industries (such as the petroleum industry) to refer to all relief devices in general.