magnetic quantum number

The magnetic quantum number $m_l$ identifies specific orbital in a subshell. For a given azimuthal quantum number $l$ (subshell shape), possible $m_l$ ranges from $-l$ to $l$ in integral increments (including $0$), e.g. for $2\mathrm{p}$ subshell ($l=1$), there are 3 orbitals ($m_l=-1$, $0$, or $1$) and $3\times 2=6$ electrons.