What are coastlines?

A coastline is where the land meets the sea, like a border between two friends.

Imagine you have a big bowl of water, and next to it is a pile of sand. If you pour the water onto the sand, the place where they touch becomes the coastline, kind of like how your hand touches the table when you rest it there.

Coastlines can be smooth or wiggly, just like the edges of a cookie. Some are straight, like a ruler, and others have lots of bends and twists, like a snake on a path.

Over time, waves from the sea come in and out, pushing sand around, it's like when you splash water with your toes in the pool. This can make the coastline grow or shrink, or even change shape completely!