Penance is repentance of sins, as well as the name of the Catholic Sacrament of Penance and Reconciliation/Confession. The word penance derives via Old French penance from the Latin poenitentia, the same root as penitence, which in English means repentance, the desire to be forgiven, see contrition; in many languages only one single word is derived. Penance and repentance, similar in their derivation and original sense, have come to symbolize conflicting views of the essence of repentance, arising from the controversy as to the respective merits of "faith" and "good works." doing public penance at Attigny in 822]]
Sacramental penance
In a sacramental understanding of the term, "penance" applies to the whole activity from confession to absolution. Generally speaking, however, it is used to characterize the works of satisfaction imposed or recommended by the priest on or to the penitent. Traditionally, penance has been viewed as a punishment (the Latin poena, the root of pen(it)ance,
Source:
http://en.wikipedia.org/wiki/Penance