I'd like to know if there exists an established name for a set $T \subset \mathbb{R}^n$ with the following property:
For every $x \in T$ there exists a convex set $C \subset T$ such that $x \in C$ and $\lambda(C) > 0$
where $\lambda$ is the Lebesgue measure.
Intuitively, what I am trying to describe is a set that "has volume everywhere", such that a point $x \in T$ can be moved a small distance in any of $n$ independent directions and still remain inside $T$.