General-ish texture/ mesh question: Parallax?

[ButchDiavolo]

While browsing Nexus, I keep seeing mods that mention parallax. I am completely unversed in graphical subjects, so I have no idea what is meant by that. What does parallax do and is it a good idea to use it in combination with the STEP 2 guide? Bearing in mind that I deviated from the guide enough that I don't use the STEP patches. Can someone please explain to me in 5 year old child terms?

[DoubleYou]

Parallax provides a fake 3d effect on 2d textures. You have to tweak your setup accordingly to maintain visual compatibility, or it can look buggy.