An event is something that happens instantaneously at a single point in spacetime, such as a light flashing, or a position on a moving object passing another point.

All events in spacetime are defined using the four coordinates t, x , y, z.

It is often referred as xμ using index notation, with μ = {0,1,2,3}

The quantity xμ is known as the four-position (it is one example of four-vector) as it describes an event or position in spacetime using the four components (ct,x,y,z).

We can think of a particule moving through spacetime as a succession of events, and if we link all these events together we would obtain a line representing the particle's travel through spacetime. This line is called the particle's world line.