A 3D shape, or a three-dimensional shape, is a solid figure that has three dimensions: length, width, and height. This means you can see how thick or deep the shape is, unlike a flat 2D shape, which only has length and width.
Think of it like this: imagine a box. It has a length (the long side), a width (the short side), and a height (how tall it is). This makes it take up space in our world. 3D shapes can be things we see every day, like a soccer ball (which is round), a cube (like a dice), or a pyramid (like the ones in Egypt).
In summary, 3D shapes are objects we can hold, touch, and measure all around us, and they have an extra dimension that makes them feel real and full!