For centuries, the faithful of Russia have honored Sts. Peter and Fevronia as patrons of honorable marriage.  A few years ago, the Day of Family, Love and Fidelity, in honor of Orthodox family life, was established, fittingly acknowledging these righteous saints as protectors.  On this day, special petitions for the preservation of Orthodox marriage are included in the Liturgy and a special prayer, invoking the intercession of Sts. Peter and Fevronia, is said at the conclusion of the service. (This prayer is included at the end of the Akathist.)

What is an Akathist?  An akathist (Greek, akathistos) is a hymn dedicated to a saint, holy event, or one of the persons of the Holy Trinity. The word akathist itself means "not sitting." (Source:  https://orthodoxwiki.org/Akathist)