• $\Psi$ is the wave function,
• $m$ the mass of the particle,
• $q$ the charge of the particle,
• $\vec{\sigma}$ the Pauli matrices,
• $\vec{p}$ the momentum,
• $\vec A$ the vector potential,
• $\phi$ the electric scalar potential and
• $\hbar$ the reduced Planck constant.

Take note that $\vec \sigma$, a "vector of matrices" is only used as a convenient short-hand notation for the sums that appear in the equation. For example, $\vec \sigma \vec p = \sigma_1 p_1 + \sigma_2 p_2 + \sigma_3 p_3. $