Sine populo (Latin for "without the people") is an expression that is used in the Roman Rite liturgy to describe a Mass celebrated by a priest without a congregation.
Corresponding to the latter form, the Missal presents the Ordo Missae cuius unus tantum minister participat (literally, Order of Mass in which only one server participates).
[5] Citing Joseph Jungmann's work on the origin of the Roman Rite, Rausch says that the celebration of private masses is traceable to the 6th century,[6][7] and O'Loughlin identifies practices associated with it within the Dialogues of Pope Gregory the Great (sed 590-604).
[4] Decrees were issued against solitary celebration by the priest alone, requiring the assistance of at least two persons, so as to justify the use of the plural in liturgical formulas such as Dominus vobiscum.
"[11] In the 16th century, the Protestant Reformers expressed opposition to any Mass without a congregation, but the Council of Trent defended the then existing practice.