The Weyl equation is invariant under the action of the Lorentz group. This means that, as boosts and rotations are applied, the form of the equation itself does not change. However, the form of the spinor ψ ψ itself does change. Ignoring spacetime entirely, the algebra of the spinors is described by a (complexified) Clifford algebra. The spinors transform under the action of the spin group. This is entirely analogous to how one might talk about a vector, and how it transforms under the rotation group, except that now, it has been adapted to the case of spinors.