$\mathrm{Fe}{}_{0.95}\mathrm{O}$ is an example of

There is less than one $\mathrm{Fe}$ per $\mathrm{O}$, and charge balance is kept by some $\mathrm{Fe}{}^{2+}$ being oxidised to $\mathrm{Fe}{}^{3+}$. This is a non-stoichiometric metal deficiency defect.