Pax vobiscum is a Latin salutation that means "peace be with you." It's common to hear pax vobiscum during a Catholic mass.
The Latin phrase pax vobiscum translates literally as "peace with you." It and pax vobis, "peace to you," are together known as "the Pax" in the Catholic church and some other Christian denominations. These greetings, which are taken from the New Testament of the Bible, are used in various religious ceremonies.