Here's why:

* Fats are triglycerides, a type of lipid composed of glycerol and three fatty acid chains.

* Fatty acids can be saturated or unsaturated.

* Saturated fatty acids have no double bonds between their carbon atoms, making them straight and able to pack tightly together. This tight packing results in a higher melting point, meaning they are solid at room temperature.

* Unsaturated fatty acids have one or more double bonds in their structure, causing them to be less tightly packed and have a lower melting point, making them liquid at room temperature (oils).

So, while all fats are lipids, not all lipids are fats. Oils, for example, are also lipids but are liquid at room temperature due to their higher proportion of unsaturated fatty acids.