The answer is a pure substance.
Pure substance can also be divided into compounds or elements, they both cannot be separated by physical methods. And elements, cannot be further separated by chemical methods. Physical methods may include distillation, crystallization, evaporation etc.
Compunds are made up of 2 or more elements chemically combined together, though it can be separated using chemical methods such as heat or electricity.
But as these both compounds and elements cannot be separated by physical methods, they're called pure substance. Unlike mixtures, which can be separated using physical methods.