Particle

A particle is anything which:

• Has negligible dimensions (doesn’t take up any size).
• The direction of acceleration is the direction of the force applied (no spinning).
• Cannot be stretched.
• …Among some other assumptions.

In physics, we usually talk about particles as any sort of (usually small) matter or sometimes unit of energy (e.g. a photon).
They’re the fundamental building blocks of everything.

We can model mechanics problems as particles, to simplify them.