One philosopher said this is the one thing that makes something a 'mind'

Franz Brentano argued that every mental state is 'about' something — a belief is about a fact, a fear is about a danger, a wish is about an outcome — even when that something doesn't exist, like a wish for a unicorn. He called this 'aboutness' intentionality and proposed it as the one mark that separates mental states from purely physical ones.

— Franz Brentano, Psychology from an Empirical Standpoint — 1874