A quark is one of the tiniest building blocks of matter in the universe, far smaller than anything you can see even with the most powerful microscope. Scientists discovered that atoms, which make up everything around you, contain even smaller particles called protons and neutrons. And those particles are made of quarks.

Think of it like this: if you could zoom in on a grain of sand, then zoom in on one atom in that grain, then zoom in on the nucleus at the center of that atom, you'd finally reach quarks. They're so incredibly small that scientists can't observe them directly. Instead, they detect quarks by smashing particles together at tremendous speeds in massive machines called particle accelerators and analyzing what happens.

Quarks come in six types, which physicists whimsically named “flavors”: up, down, charm, strange, top, and bottom. The most common quarks are the up and down varieties, which combine in groups of three to form protons and neutrons. A proton contains two up quarks and one down quark, while a neutron contains two down quarks and one up quark.