The Feast of the Annunciation is generally observed on March 25, nine months before Christmas and the date celebrating the birth of Jesus. The Feast of the Annunciation commemorates the “announcement” by the angel Gabriel to Mary that she had conceived and would bear the Christ child (Annunciation is anglicised from the Latin Vulgate Luke 1:26-39 Annuntiatio nativitatis Christi).
The story of the Annunciation is contained in Luke 1 26-38; the very first verse of which states that the Annunciation occurred “in the sixth month” of Elizabeth’s pregnancy with John the Baptist. A separate shorter annunciation than that in Luke occurs in Matthew 1:18-21, in which Gabriel tells Joseph that Mary will bear Jesus.
Here’s the text of Luke 1 26:39 in the Wycliffe Middle English translation (c. 1382 to 1395).
26 But in the sixte moneth the aungel Gabriel was sent fro God in to a citee of Galilee, whos name was Nazareth, 27 to a maidyn, weddid to a man, whos name was Joseph, of the hous of Dauid; and the name of the maidun was Marie. 28 And the aungel entride to hir, and seide, Heil, ful of grace; the Lord be with thee; blessid be thou among wymmen. 29 And whanne sche hadde herd, sche was troublid in his word, and thouyte what maner salutacioun this was. 30 And the aungel seide to hir, Ne drede thou not, Marie, for thou hast foundun grace anentis God. 31 Lo! thou schalt conceyue in wombe, and schalt bere a sone, and thou schalt clepe his name Jhesus. 32 This schal be greet, and he schal be clepid the sone of the Hiyeste; and the Lord God schal yeue to hym the seete of Dauid, his fadir, and he schal regne in the hous of Jacob with outen ende, 33 and of his rewme schal be noon ende. 34 And Marie seide to the aungel, On what maner schal this thing be doon, for Y knowe not man? 35 And the aungel answeride, and seide to hir, The Hooly Goost schal come fro aboue in to thee, and the vertu of the Hiyeste schal ouerschadewe thee; and therfor that hooli thing that schal be borun of thee, schal be clepid the sone of God. 36 And lo! Elizabeth, thi cosyn, and sche also hath conceyued a sone in hir eelde, and this moneth is the sixte to hir that is clepid bareyn; 37 for euery word schal not be inpossible anentis God. 38 And Marie seide, Lo! the handmaydyn of the Lord; be it don to me aftir thi word. And the aungel departide fro hir. 39 And Marie roos vp in tho daies, and wente with haaste in to the mounteyns, in to a citee of Judee.
Art based on the Annunciation often shows Mary reading, either in a sitting room or a garden, lilies, and a sunbeam which symbolizes the divine conception. See for example the central panel of the Robert Campion Merode Altar piece above. If you look closely at the top left, there’s an image of an tiny figure sliding in on a sunbeam, carrying a cross. Mary is shown reading a book, perhaps a psalter, and there are lilies on the table (this barely touches the iconography used in this image, and of the Annunciation in general).
The Annunciation is a particularly popular subject for miniatures and full page illustrations in Psalters and Books of Hours, most often as one of the illustrations for the Hours of the Virgin.