This quote is taken from a math.SE answer (https://math.stackexchange.com/a/622695/816960):
By the way, for Euclidean vector spaces, there is a canonical isomorphism, given by $V \to V^*$, $v \mapsto \langle v, -\rangle$.
What does the dash in this inner product mean? I've never seen this notation before? I assume it's some kind of placeholder, but for what I can't guess.