The orientation in space of the electron is described by which quantum number?

Magnetic quantum number.

Explanation:

Orbitals with the same principal quantum number and the same l value belong to the same subshell.

The magnetic quantum number, ml distinguishes the orbitals available within a subshell, and is used to calculate the azimuthal component of the orientation of space.

The value of ml can range from - ℓ to + ℓ. The s, p, d, and f subshells contain 1, 3, 5, and 7 orbitals each, with values of m within the ranges 0, ±1, ±2, ±3 respectively while containing 2 different spin electrons.