The top quark is a particle of matter. It is one of the six quarks in the standard model and is considered to be an elementary particle in our current state of knowledge.
The top quark is one of the six quarks, the others being:
The top quark
Like its companions it is a fermion; it has a fractional electrical charge equal to ⅔ e. It is often abbreviated to t quark. It was not one of the first three quarks postulated at the beginning of the 1960s independently by Gell-Mann, Yuval Ne'eman and George Zweig to understand and classify the hadrons that were known at the time. It is much heavier than these quarks and has a mass almost as heavy as a gold nucleus.
Two of the discoverers of quark theory. © universe-review
The top quark was directly observed in the CDF experiments in 1994, followed by DØ in 1995, at the Tevatron (Fermilab). It belongs to the third generation of particles in the standard model.
Its existence had been postulated in 1973 by Makoto Kobayashi and Toshihide Maskawa to explain the CP violation observed in the disintegration of kaons. Like the other quarks, it is sensitive to the strong nuclear interactions described by quantum chromodynamics.
The table of elementary particles in the standard model which includes the top quark. © MissMJ, Wikipedia