# Square bracket notation of the basis of 16 independent gamma matrices

The question is very simple and I couldn't find an answer.

What the notation $$\gamma^{ [ \mu} \gamma^{\nu} \gamma^{\rho ]}$$ and $$\gamma^{ [ \mu} \gamma^{\nu} \gamma^{\rho} \gamma^{\sigma ]}$$ means?

(From Peskin and Schroeder page 49)