Electrons, quarks, and gluons are classified as elementary particles, meaning they are indivisible and not composed of smaller components. The discussion revolves around whether these particles can be considered as composed of "nothing" or if they are fundamentally made of something, such as quantum fields. It is clarified that while these particles possess properties like mass and charge, they do not have a substructure or composition in the traditional sense. The concept of being "composed of energy" is debated, with the consensus being that energy is a property rather than a constituent. Ultimately, the nature of elementary particles remains complex, with ongoing discussions about their fundamental characteristics and the implications of quantum physics.