Formerly, on major Sundays and feast days, the clergy and people of Rome would gather at specific churches where the Pope would celebrate the Office and Mass. These churches were designated as the “station” church for that day. Authors do not agree on the origin of this term, but one explanation is that “station” was a military term which was applied to the gathering of the soldiers of the Church Militant. On certain days, there would be a procession to the station church from another church, which was called the “collect” church as this was where the procession was “collected” or assembled. This practice predates Pope St. Gregory the Great (d. 604).
In some cases, the traits of the liturgy decided the selection of station (e.g. the station for the first Mass of Christ is St. Mary Major at the Altar of the Crib). In other cases, it seems the choice of the station influenced the liturgy (e.g. the station for Sexagesima Sunday is at St. Paul’s Outside the Walls and St. Paul is referenced in the Collect).
The station churches are still listed in the Extraordinary Form Roman Missal where their influence is still present.