Ordinal described by a first-order formula

A first-order formula $\phi$ describes an ordinal $\alpha$ when $\alpha$ is the least ordinal such that $V_{\alpha }\models \phi$. No strongly inaccessible cardinal can be described: if $V_{\kappa }\models \phi$, the Lévy reflection theorem produces some $\alpha <\kappa$ with $V_{\alpha }\models \phi$.