Projection refers to the process of translating three dimensional information into a two dimensional representation in an image.

There are many different types of projections, the broadest classification divides them into perspective and parallel projections.

In perspective projection, lines that are parallel in the three dimensional information will converge towards a vanishing point in the two dimensional representation whereas in a parallel projection such lines stay parallel in the two dimensional representation.

further reading:

• Graphical Projection
• Floor Plan
• Multiview Orthographic Projection