In particle physics, the term particle zoo is used colloquially to describe a relatively extensive list of the then known “elementary particles” that almost look like hundreds of species in the zoo.
In the history of particle physics, the situation was particularly confusing in the late 1960s. Before the discovery of quarks, hundreds of strongly interacting particles (hadrons) were known. It was later discovered that they were not elementary particles, but rather composites of the quarks. The set of particles believed today to be elementary is known as the Standard Model.
Michel van Biezen from ILectureOnline.com explains how many particles there are and what they do. Of the more than 400 subatomic particles most of the matter is created by a number of 20 or so elementary subatomic particles. The rest are composite particles.