A diagram is a simple drawing that explains how something works, shows how parts connect, or makes information easier to understand. Unlike a detailed picture that shows what something looks like, a diagram strips away unnecessary details to focus on the important parts.

Think of a diagram as a visual explanation. When you draw a diagram of the water cycle, you might use arrows to show how water evaporates from the ocean, forms clouds, falls as rain, and flows back to the sea. A diagram of a plant cell shows the nucleus, cell wall, and other parts labeled clearly, even though a real cell is far too small to see without a microscope.

Scientists use diagrams to explain experiments. Architects use diagrams to plan buildings. Students use diagrams to organize ideas before writing essays. A basketball coach might diagram a play on a whiteboard, drawing X's and O's to show where each player should move.

A good diagram uses lines, shapes, labels, and sometimes arrows to mark out the essential information. When you diagram a sentence in English class, you're drawing lines to show how words relate to each other. A diagram transforms complex information into something you can see and understand at a glance.