A post-starburst galaxy (PSB galaxy) is a galaxy which
is thought to have been a starburst galaxy some time back:
the characteristic is they lack the wavelengths of OB stars,
but still show considerable emission of the wavelengths of
A-type stars and F-type stars, which remain for a longer
time subsequent to their formation.
Other terms are E+A galaxy, the E for elliptical galaxy and
the A for A-type stars (atypical for ellipticals), and K+A galaxy,
the K for K-type stars because the galaxies also show their
wavelengths, presumed to come from K-class giant stars,
whose presence also indicates considerable somewhat-recent
star formation.