What is "dominus vobiscum"

interj. (context Roman Catholicism English) A devout salutation often used as a prelude to certain set prayers; the traditional response is ''Et cum spiritu tuo''.

Dominus vobiscum ( Latin: "The Lord be with you") is an ancient salutation and blessing traditionally used by the clergy in the Roman Catholic Mass and other liturgies, as well as liturgies of other Western Christian denominations.