Penitential Psalms or Psalms of Confession, is a name given from very early times to Psalms vi., xxxii., xxxviii., li., cii., cxxx., which are specially expressive of sorrow for sin. The name belonged originally to the fifty-first Psalm, which was recited at the close of daily morning service in the primitive Church.
Definition taken from The Nuttall Encyclopædia, edited by the Reverend James Wood (1907)
Peninsular War * Penitents, Order Of