My questions should be rather simple. I was trying to get through one of my professor’s papers, and I saw the following notation, first with regards to Dirac and Weyl spinors, but the notation continues throughout $$ \psi=\begin{pmatrix}\lambda_\alpha\\\bar\lambda^{\dot\alpha}\end{pmatrix} $$

In the $\bar\lambda^{\dot\alpha}$ term, what does the dot over the $\alpha$ signify?