A lattice girder looks like a big, strong web made out of metal or wood. It's like a really tough spiderweb that is used to support things like bridges and buildings. Imagine if you have ever played with those building blocks that snap together using long sticks and little connectors. A lattice girder is kind of like those sticks and connectors, but on a much bigger scale. Each little piece in the girder is important because they all work together to make it super strong. When you see a lattice girder, it might look like a bunch of tiny squares or triangles all connected together. The girder is designed this way because it can support a lot of weight without being too heavy. If we didn't have lattice girders, we wouldn't be able to build big, strong structures that can stand up to lots of heavy things.