What is the difference between orthogonal, complementary, null, perpendicular, and such?

What is the opposite of orthogonal?

Lot of geometry references and I'm having trouble getting a grasp of the essence of orthogonality, it seems.

Also keep seeing perpendicular but what the heck does that mean in conceptual or real life analogies? Wall and floor but again, what the heck does that mean in practical terms?

I initially thought it was like two points being on a same axis but not the same pair of coordinates or in conceptual terms, two things that are points on the same spectrum/axis like in a range from 1-100 or something but it seems like its on two arbitrary points on like a seperate x/y axis so like what is the point of it or where is the actual relationship?