The Local Standard of Rest (LSR) is the mean motion of material in the Milky Way in the neighborhood of the Sun. When an object's Radial Velocity is cited, for example, the measure can be relative to the observer, which would depend upon the spin and orbit of the Earth, or relative to the Sun, or relative to the LSR, or relative to the Galactic Center of the Milky Way.
The LSR Velocity with respect to the galactic center has been recently estimated as 255 km/s.
Galactic All-Sky Survey (GASS)
High-Velocity Cloud (HVC)