math.la.t.vec.projection…

 
The (orthogonal) projection of a vector onto a subspace is the point in the subspace closest to the vector. math.la.t.vec.projection.closest
The projection of a vector which is in a subspace is the vector itself. math.la.t.vec.projection.element
A vector can be written uniquely as a sum of a vector in a subspace and a vector orthogonal to the subspace. math.la.t.vec.projection.subspace