I'm going to explain it without actually knowing what it is, then google it, then get back to you.

Ok, so, a normal map is a version of the image that calculates roughness using the different shades of blue for a more precise reading of a roughness scale.

Here's what I found on Blender's site

The Normal Map node generates a perturbed normal from an RGB normal map image. This is usually chained with an Image Texture node in the color input, to specify the normal map image. For tangent space normal maps, the UV coordinates for the image must match, and the image texture should be set to Non-Color mode to give correct results.

So yeah I was completely wrong.