Maximum circular velocity $V_{max}$ is a characteristic of the mass of a dark matter halo. It is defined as a maximum value of the circula velocity: where $M(<r)$ is the mass within the sphere with the radius $r$ and $G_N$ is the Newton's constant. The radius $r_{max}$ such that $V_{max} = v_c(r_{max})$ determines the concentration of the mass distribution.
This quantity can be defined independently of the halo density profile.