...I'll give it a try...... A heat resistance temp.as it pertains to silicone would be the temperature range that the silicone is able to maintain its properties and structure. There is silicone grease and silicone oil that would behave in much the same matter as any grease or oil that you may be familiar with......too cold and they thicken up and don't properly lube...too hot and they loose their viscosity and break down. Silicone rubber, resin and caulk in their solid form do better in cooler temps. but loose their properties and structure at 500'f. As an example....the last automotive engine that I built, I used Permatex gasket sealer,a high temp. RTV silicone good for 500'f. If that engine mechanically has an issue and starts heating up to that 500'f point , the gasket sealer starts to fail and now you have a several hundred pound grenade ready to explode. Excessive cold temps. could cause the silicone to shrink, depending on application and type of silicone used.
A heat deflective temp. according to Wikipedia is "The temperature at which a polymer or plastic sample deforms under a specified load. This property of a given plastic material is applied in many aspects of product design, engineering and manufacture of products using thermoplastic components." So different plastics or polymers will start to deform at different temperatures. A plastic patio chair can withstand you sitting in it when its a 100'f+ outside. A plastic model car would begin to warp and melt in the same heat. The chair was engineered to be kept outside during the hottest part of summer....the model kit ,made of #6 styrene plastic, was engineered to be assembled and displayed on a shelf at room temperature.