It represents distance traveled, essentially, but is slightly more complicated because this is about rotation and area.

Imagine going

*through* a tunnel. You are passing from one end to the other.

But it can be used for unenclosed spaces. You can pass through the countryside.

That's one dimensional travel along a line. You go over the ground following a thin line.

Now imagine a whole line traveling perpendicular to the direction of movement. Say you are driving a harvester through a field of wheat. It sweeps

*through* an area as it moves. It covers an area, not just a line.

Now if that harvesters starts turning, then the area it sweeps through will be in the form of a circle. The total angle the harvester turns can be measured.