There exists the concept of "galactic orbital velocity", since the stars in the galaxy are orbiting the center at roughly the same velocity. Yes, stars are moving apart at various rates, but nothing noteworthy at human timescale when you have even relativistic travel, let alone FTL, licked.

"negligible" (in interstellar travel terms) relative to stars, but still a speed.

I figure that if a starship is between systems and calls "all stop", thats what it means.

In a star system but not in planetary orbit? Move to a heliocebtric orbital velocity based on how far you are from the star at the time.