What Does “Vigil Mass” Mean?

A question from someone with a Church of Ireland background: what does the term "vigil" mean — and is it another name for a service?

The Church Counts a Liturgical Day from Sunset, Not Midnight
This follows ancient Jewish tradition. Because of this, the Sunday celebration begins on Saturday evening. So when a person attends Mass after a certain time on Saturday (usually 4:00 p.m. or later), this is liturgically celebrating Sunday—even though the civil calendar still says Saturday.

• It uses Sunday prayers
• It uses Sunday readings
• It celebrates Sunday liturgically

• Work Sundays
• Have family or care duties
• Need flexibility

In relation to Services, while Mass is most commonly celebrated in Catholic churches, other Services include:

• The celebration of Sacraments
• Liturgy of the Hours (Morning Prayer, Evening Prayer etc), but only some parishes will celebrate these publicly, and then usually at certain times of the year and on weekdays
• Eucharistic Devotions, such as Benediction, Eucharistic Adoration Services
• Liturgy of the Word in the absence of Clergy - which is celebrated in some parishes
• Other Services, often seasonal, such as public Rosary, Stations of the Cross