What does not perpendicular mean?

What does not perpendicular mean is when two things are not at a perfect right angle, like the corner of a square.

Imagine you're playing with building blocks. If you put one block next to another and they form a neat, square corner, that’s perpendicular, just like the walls in your room meet at a perfect right angle.

But if you tilt one block so it doesn’t make that clean corner anymore, that’s not perpendicular. It's more like when you lean against the wall instead of standing straight up, your body and the wall aren't forming a perfect square corner.

Think about a fence in your backyard. If the posts are all lined up so each section is at a right angle, that’s perpendicular. But if one part slants or leans, like when the wind pushes it sideways, then those parts of the fence are not perpendicular, they're more like a crooked line than a perfect corner.

So, not perpendicular just means things aren’t meeting at a perfect right angle, like a messy corner instead of a tidy one.