Question

what is the difference between projection to a subspace of vectors and a subspace of orthogonal vectors

Answer 1

In a parallel projection, points are projected (onto some plane) in a direction that is parallel to some fixed given vector. In an orthogonal projection, points are projected (onto some plane) in a direction that is normal to the plane. So, all orthogonal projections are parallel projections, but not vice versa.

Explanation: