As already mentioned, it's for honing. The difference is that sharpening involves removing metal to create a new edge, while honing simply bends the edge back to being straight. Although we think of steel as being a hard material, the edge of a knife is thin enough that it gets bent to one side or the other just through normal use. Using a honing rod to push the steel back to where it belongs means the knife feels sharper because you're now cutting with the actual edge.

It's not, it's for honing

It's a honing rod or honing steel. Honing isn't exactly the same thing as sharpening, but yes it will help the knife cut better.

I've heard it explained that honing is for improving the cutting edge you have, and sharpening is cutting a new edge.