Recessional velocity is the rate at which an extragalactic astronomical object recedes (becomes more distant) from an observer as a result of the expansion of the universe.
The recessional velocity of a galaxy can be calculated from the redshift observed in its emitted spectrum.
One application of Hubble's law is to estimate distances to galaxies based on measurements of their recessional velocities.
However, for relatively nearby galaxies the peculiar velocity can be comparable to or larger than the recessional velocity, in which case Hubble's law does not give a good estimate of an object's distance based on its redshift.
is negative (i.e., the galaxy's spectrum is observed to be blueshifted) as a result of the peculiar velocity.