Short-lived particles are subatomic particles that exist for a very short period of time before decaying into other particles. Pions (5 letters) are a type of meson, which is a particle composed of one quark and one antiquark. They are the lightest mesons and can be either positively or negatively charged. Taus (4 letters) are leptons, which are particles that do not interact with the strong force. They are the heaviest of the three leptons and have a negative charge.