Magnificat is the Latin name of the canticle of Mary, the mother of Jesus, which she speaks to Elisabeth the husband of Zechariah that she is pregnant with the Saviour Jesus Christ. It appears in the Gospel of Luke, I:46-55

Latin:

Magnificat anima mea Dominum
Et exultavit spiritus meus in Deo salutari meo.
Quia respexit humilitatem ancillæ suæ: ecce enim ex hoc beatam me dicent omnes generationes.
Quia fecit mihi magna qui potens est, et sanctum nomen eius.
Et misericordia eius a progenie in progenies timentibus eum.
Fecit potentiam in bracchio suo, dispersit superbos mente cordis sui.
Deposuit potentes de sede et exaltavit humiles.
Esurientes implevit bonis et divites dimisit inanes,
Suscepit Israel puerum suum recordatus misericordiæ suæ,
Sicut locutus est ad patres nostros, Abraham et semini eius in sæcula. (Vulgate)

English:

My soul doth magnify the Lord,
And my spirit hath rejoiced in God my Saviour.
For he hath regarded the low estate of his handmaiden: for, behold, from henceforth all generations shall call me blessed.
For he that is mighty hath done to me great things; and holy is his name.
And his mercy is on them that fear him from generation to generation.
He hath shewed strength with his arm; he hath scattered the proud in the imagination of their hearts.
He hath put down the mighty from their seats, and exalted them of low degree.
He hath filled the hungry with good things; and the rich he hath sent empty away.
He hath holpen his servant Israel, in remembrance of his mercy;
As he spake to our fathers, to Abraham, and to his seed for ever. (KJV)

In Latin or in English, the text has been a favourite of many composers and forms a part of the Roman Catholic Vespers service and also the Anglican Evensong service.