Final answer:
'Haec dies' is a Latin phrase commonly used in Christian liturgy and hymns during the Easter season to signify the joy and celebration of the resurrection of Jesus Christ.
Step-by-step explanation:
'Haec dies' is a Latin phrase that translates to 'This is the day' in English. It is a phrase commonly used in Christian liturgy and hymns, particularly during the Easter season. The phrase signifies the joy and celebration of the resurrection of Jesus Christ. It is often associated with the liturgical texts and music of the Easter vigil and Easter Sunday services.