The fermions are a class of elementary particles that are defined by their 1/2 integer spin, and the fact that they make up the matter that we interact with everyday.
Fermions include both particles of matter and anti-matter. Particles of matter and their corresponding particles of anti-matter will annihilated if they come into contact. This results in the release of the energy bound by the particles. The fermions are further divided into two categories: quarks and leptons. Quarks were named after the appearance of a nonsense word in the book "Finnigan's Wake" by James Joyce since these particles were considered so odd by the scientists that discovered them. Both quarks and leptons are divided into three "generations" based on their mass and stability (in general, the heavier the particle, the less stable it is).
The first generation of quarks includes of the up and the down quarks, as well as the antiup antiquark and the antidown antiquark. The names up and down as well as the names for the other quarks are rather arbitrary and have nothing to do with the physical properties of the quarks. The pairing of the names do help with remembering that quarks are in the same generation. The up quark has an electric charge of +2/3, while the down quark has a charge of -1/3. The up quark is about half as massive as the down quark. A proton is made of two up quarks and one down quark, giving it a charge of +1 making it positively charged. A neutron is made of two down quarks and an up quark giving it no charge at all.
The second generation of quarks includes the strange and charm quarks, as well as the antistrange antiquark and the anticharm antiquark. The strange quark like the up quark, has a charge of +2/3, but is about a hundred times more massive than the up quark. The charm quark like the down quark, has a charge of -1/3 and is about a thousand times more massive than an up quark.
The third generation of quarks includes the bottom and top quarks, as well as the antibottom anitquark and the antitop antiquark. The bottom quark is also know as the beauty quark, and the top quark is also known as the truth quark. The bottom quark has a spin of +2/3, and the top quark has a spin of -1/3. The bottom quark is about four thousand times more massive than the up quark, while the top quark is about one hundred seventy thousand times more massive than the up quark - almost as massive as the entire nucleus of an atom of gold. Second and third generation quarks aren't nearly as stable as first generation quarks, and decay rapidly into first generation quarks.
