Three-Dimensional. A shape or object which has height, length and width. This is anything that we can hold in the real world.

Example: Cube, Cuboid, Any Prism, Sphere, and many more. 

🔑Key 3D Topics: Naming Shapes, Nets, Properties of 3D Shapes
👀Also Look up: 2D, Prism, Surface Area, Volume

Two-Dimensional. A name usually given to a flat shape that can only be drawn, not held.

Example: Square, Rectangle, Triangle, Parallelogram, Trapezium, Pentagon, Hexagon and many more. 

🔑Key 2D Topics: Naming Shapes
👀Also Look Up: 3D, Area, Perimeter, Polygons, Surface Area