Presider and celebrant are synonyms for the person who offers the Mass. Thus, only a priest or bishop can be a presider or celebrant. Presider is a newer term that generally indicates that the priest takes the lead in offering the Mass. Celebrant is of older vintage and connotes that the priest is the person who primarily celebrates the Mass. In recent times presider has become preferred by some as a means of indicating that the congregation should take an active role in the liturgy, proper to their status as laity. Either term is correct.