Lath is like a special kind of fence made out of thin pieces of wood. Imagine you have a big piece of paper and you cut it into very skinny strips. Now, take those strips and hold them close together, side by side. That's what lath looks like!
People use lath to cover walls or ceilings. But why would we use it instead of just a regular piece of wood? Well, lath can bend and flex a little bit more than regular wood. This makes it really good for covering a curvy or bumpy surface, like the inside of an old house.
Once the lath is in place, you can put a special kind of plaster or stucco on top of it. The plaster will stick to the lath, kind of like glue. When it dries, it makes a hard and smooth surface that looks really nice. So, lath is kind of like the foundation of a fancy wall or ceiling!