In Class 7 Mathematics ICSE, the representation of 3D objects in 2D involves learning about different methods such as drawing projections, isometric drawings, and orthographic projections.

1. **Projections**: Students learn about drawing the projection of 3D objects on a 2D plane. This includes understanding how to draw the top, front, and side views of an object.

2. **Isometric Drawings**: Isometric drawings are used to represent 3D objects on a 2D surface. Students learn to draw objects using isometric grids and understand how to maintain the correct proportions.

3. **Orthographic Projections**: Orthographic projections involve representing 3D objects using multiple 2D views. Students learn to draw the front, top, and side views of an object to visualize its complete structure.

Overall, the focus is on developing the ability to visualize and represent 3D objects accurately in 2D, which is an important skill in geometry and engineering graphics.