The term "smallest particle" can be understood in a couple of different ways, depending on the context.
In terms of the smallest known fundamental particles of matter, the current understanding in particle physics is that quarks and leptons are the elementary particles that make up matter. Quarks are believed to be the building blocks of protons and neutrons, while leptons include particles such as electrons and neutrinos. According to our current knowledge, quarks and leptons are considered to be point-like particles, meaning they have no spatial extent and are indivisible.
However, it's important to note that our understanding of the smallest particles is based on the best theories and experimental evidence available to us at the present time. Future discoveries and advancements in scientific knowledge could reveal new particles or substructure within the known particles, leading to a deeper understanding of the fundamental building blocks of matter.
Additionally, in the context of particle physics, there are other types of particles such as gauge bosons (like photons and W and Z bosons) and the Higgs boson, which play important roles in fundamental interactions. These particles are not considered to be elementary, as they arise from quantum fields and interactions within the framework of particle physics.
Therefore, while our current understanding points to quarks and leptons as the smallest known particles, the possibility of future discoveries or refinements in our understanding always remains open. Science is an ongoing process of exploration and discovery, and our knowledge and understanding of the fundamental particles may evolve as we delve deeper into the mysteries of the universe.