Answer: orbital shape.
1) There are four quantum numbers to describe the electrons. These are:
i) Principal quantum number (n)
ii) Azimuthal quantum number (ℓ), also called angular momentum quantum number.
iii) Magnetic quantum number (m)
iv) Spin quantum number (s)
2) The principal quantum number tells the main energy level. It can be 1, 2, 3, 4, 5, 6, 7. It is related with the orbial size. 1 is a small orbital, 7 is a big orbital.
2) The Azimuthal quantum number (ℓ) or angular momentum quantum number may be a number between 0 and n - 1.
It tells the kind of orbital, which is its shape
The correspondence is:
0 = s orbital,
1 = p orbital,
2 = d orbital,
3 = f orbital.
3) Magnetic quantum number (m) tells the orientation. It can be from - ℓ to + ℓ
For example when ℓ = 1, the orbital is p, and the magnetic quantum number may be -1, 0, or +1, which correspond to px, py, pz: the orientation of the p orbital in the space.
4) Spin quantum number (s) can be either +1/2 or -1/2.