As far as I know a point in space is shown by it's t,x,y and z coordinates? Anyway it isn't so much how it's defined that I'm interested in, it's more about what a point of space is. Let's say we took a 1cm^2 region of space, how many unique points of space does this region have? What distinguishes one point in space to another point? Is there a fundamental limit as to how small the distance can be from point a to point b? I heard planck length being thrown around a bit but I don't really understand it, is this the smallest physical distance that can exist or just the smallest physical distance we can measure? Basically what I want to know is if you take two points on a straight line, how many unique points exist between them?