Definition of the mean curvature of the boundary of a smooth domain $\Omega \in \mathbb{R}^n$

Question

In some papers and notes on differential geometry, I found the statement like

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Let $\Omega \subset \mathbb{R}^n$ be open, smooth, convex such that its boundary $\partial \Omega$ has non-negative mean curvature $H[\partial \Omega] \geq 0$...

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I am wondering what is the precise definition of the mean curvature of $\partial \Omega$. For instance, if we take $\Omega = [0,1]$, does its boundary $\partial \Omega = \{0,1\}$ possesses a non-negative mean curvature?