Convex describes a surface or shape that curves outward, like the outside of a sphere or dome. If you look at a basketball, the surface you see is convex: it bulges toward you. The back of a spoon is convex, curving away from the handle.

Think of it this way: if you drew a straight line between any two points on a convex shape, that line would stay completely inside the shape. A magnifying glass has a convex lens that's thicker in the middle than at the edges, which is what makes things look bigger when you look through it.

The opposite of convex is concave, which curves inward. The inside of a bowl is concave, while the outside of that same bowl is convex.

In geometry, a shape is convex if it doesn't have any dents or indentations. A circle is convex, and so is a rectangle. But a star shape isn't convex because it has those pointy indentations between the star's arms. Understanding convex shapes helps in math, science, and engineering, where the way surfaces curve affects everything from how lenses focus light to how buildings stand strong.