Question: On some days the Church calendar lists a "station." What does that mean?
Answer: The calendar lists a "station" on 89 days of the year; the ferial days of Advent and Lent, Christmas and Eastertide, and each of the Ember days. By "ferial" we mean those days on which the Mass is of the season, rather than of a particular saint. Each "station" is a church in the city of Rome. At one time the people of the City would assemble at a designated church and march in procession to the stational church. Once there, together with the pope or his delegate they would sing the solemn Mass of the day. Some of these processions and, more rarely, the papal Masses are still observed.
There are forty-five churches designated as stational churches, some of them quite old, going back to the time of the Emperor Constantine; the first to allow public Christian worship in the Empire. Yet, St. Agatha and St. Maria Nova were raised to the status of stational churches as recently as 1935. Some, for example, St. Mary Major, St. Peter's, and St. John Lateran, serve as the stational church several times a year. Only two or three of the churches are outside the walls of the City. The one called Holy Cross in Jerusalem is in the extreme eastern quarter of Rome.
Visitors to these churches on the station days may gain a partial indulgence for the visit, or a plenary indulgence if they take part in the ceremonies offered there. (Enchiridion #56) The usual conditions apply, plus the recitation of one Our Father and the Creed.