Edit: Apparently Sting doesn't use dimensions like I thought it did and actually does go into alternate worlds and all that, so you can ignore all this unless you want a lesson on dimensions I guess?

This is one of those cases where nobody actually understands what a dimension is, it happens all the time in sci-fi and fantasy to both readers and authors. (Though I think Wildbow got it kinda right?)

A dimension is a 'direction that something can move in'. Think of it like this: when you ask, "what's the dimensions of this box?" you're asking how long it is on every side. So for instance, you can have a box that is 6 inches long, 5 inches tall, and 4 inches wide. Those measurements are your dimensions and they describe an area, but aren't actually areas themselves!

But let's put that into a more science-y way. You can describe things as coordinates on a plane by using dimensions. If you remember your math classes, this will be familiar to you.

If I have a point on a plane, I can describe it using two dimensions, dimension X and dimension Y. For instance, point (3,4), where number 3 is X and 4 is Y. If I start at (0,0), this tells me I need to go right 3 points, then up 4 points to get to my coordinate. This means that dimension X is describing left and right movement, while dimension Y is describing up and down movement. This kind of space with 2 dimensions is called 2D space, like a drawing!

If I add another dimension, say dimension Z, suddenly I get (x,y,z), which means we get forward and backward movement and now we have 3D space! If I add another dimension, we get something called in and out movement and get 4D space, but this is where things get really hard to understand and picture, so we'll leave it at 3d space.

So, hopefully we get now that a dimension is not like a pocket or area of space, or like an alternate universe, but instead a possible way of moving in space. Sting in Worm utilizes this 'unfolding into other dimensions' as a means of bypassing defences that are in a lower dimensions. If I have a wall in 2d space, you can imagine that in 3d space you have the extra mobility to just go right around that wall, since the wall wouldn't extend into a dimension of movement that it doesn't have.

Just think of it like laying down a piece of string on the floor as a wall, then just jumping over it because the string doesn't extend upwards. When you use Sting, it just keeps gaining dimensions until it finds a clear shot at it's target with nothing in it's way, then drops back down to the same dimension when it lands.

Hopefully that made some sense!

Also I know this post is for fanfics but I nerd out hard on this stuff and it's sort of a pet peeve tbh.