system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is a Dimension ?

In terms of maths and physics what is a Dimension? is it just something we came up with to explain things or would Dimensions still exsit if humans didn't ( like how time would exist with out people but hours wouldn't?).
gpt
A dimension is basically a direction.

We live in three dimensions.

X, which is length.  
Y, which is height.  
Z, which is depth.

From that alone it's not terribly hard to imagine a fourth dimension in this abstract sense. It's just another direction, albeit one we can't currently see or travel.

A core aspect of dimensions is that the number of dimensions is the number of coordinates required to specify a specific location within that dimensional space.

So for example, in a 2D space (a flat plane) you need two coordinates to describe any point. (x,y). Similarly, any 3D area needs three coordinates (x,y,z). So for a four dimensional area you just need to add a fourth coordinate. (x,y,z,a).

On time: Some people consider time to be the fourth used dimension. This is because you can specify a point at a specific x, y, and z as well as time. So your four dimensional area can have points specified by (x,y,z,t), where t=time.