Regarding the atom of a chemical element, the magnetic quantum number refers to

The magnetic quantum number (ml) specifies the orientation or direction of a particular orbital in space within a given subshell. It takes integer values from -l to +l and distinguishes different orbitals (for example px, py, pz) that have the same shape and energy but point in different directions. This is distinct from the azimuthal quantum number l, which determines orbital shape, the principal quantum number n, which relates to size/energy, and the spin quantum number ms, which refers to intrinsic electron spin [2]. Thus the best choice for what ml refers to is “orientation.”

Sources

1. [1] https://nios.ac.in/media/documents/313coursee/l3.pdf
2. [2] https://www.quiz.wcd.kerala.gov.in/lPAGEw/7809Q5F/aurld/2326Q058F6/chemistry__chapter_13__electrons__in-atoms.pdf