An Akathist is a hymn the faithful stand for. The word is Greek for "not seated", and the custom of standing for it is the custom of reverence: one stands before the One praised.
The Akathist par excellence is the hymn to the Theotokos, written for the Annunciation. Its Greek original is an acrostic: its twenty-four stanzas, twelve kontakia and twelve ikoi, each begin with the next letter of the alphabet, and the ikoi are full of the greeting "Rejoice" addressed to the Mother of God. Who wrote it is uncertain; it has been ascribed to St Romanos the Melodist and to Patriarch Sergius of Constantinople, but no certain author can be named.
It is kept in Great Lent in two ways. In Greek parish use it is sung in four parts on the first four Friday evenings and whole on the fifth. In Slavic use, and in Greek monasteries, it is sung whole at Matins of the fifth Saturday, the Saturday of the Akathist. Later akathists to Christ, to the Cross, and to many saints follow the same form, and they are prayed in church and at home.