Ex-meridian

Okay kiddo, imagine a big circle that goes all the way around the world, like a belt. That's called the Earth's meridian. Now, imagine the sun is directly above that circle, shining down on it. The point where the sun is shining down on the Earth's meridian is called the noon meridian, because it's where the sun is highest in the sky at noon.

But what happens when you're not at the noon meridian? Let's say you're in a different time zone, and the sun isn't directly above you at noon. Well, the point where the sun is directly above the Earth's meridian at noon is still called the noon meridian, even though it's not where you are. The point where you are, and where the sun is directly above you at noon, is called the ex-meridian.

So basically, the ex-meridian is just the point on the Earth where the sun is shining down on it directly at noon, but it's not necessarily where the official noon meridian is. It's like your own personal noon meridian, just for your location.