The pietà was a common theme among Gothic and Medieval artists who were Christians and used religious themes because it was one of the most dramatic moments of Christ's crucifixion story. The pietà depicts a dead Jesus who has just been taken down from the cross laying across the Virgin Mary's lap, with Mary looking extremely sorrowful.

The Poor Man's Bible was a way for the largely illiterate Medieval peasantry to be able to learn Bible stories despite their inability to actually read the Bible. In many cathedrals, most notably at Canterbury Cathedral in England, the Poor Man's Bible was a giant stained-glass window that had dozens of Biblical stories that could be easily referenced by priests and parishioners alike.

"Adoration of the Magi" is an Anglicization of the Vulgate Latin phrase "a Magis adoratur," a phrase found in the Gospel of Matthew. The scene, which features three distinguished men from the East visiting the newborn Jesus, was a popular one in Medieval art, thanks to its portrayal of precious gifts, ostentatious figures, and the Christ child in one scene.

Grisaille is a type of painting done entirely in shades of gray or another neutral, monochromatic shade. By reducing the color palette to shades of gray, the artist can emulate the appearance of sculpture. It's also much less demanding on the artist, and is often used for sketches. 

The Wilton diptych is a piece of medieval art for remarkable for being a surviving example of the traveling altarpiece. Made for and featuring King Richard II of England, who ruled between 1377 and 1399, the Wilton diptych is a two-paneled piece with one side featuring the Madonna and Child surrounded by angels, facing Richard with three saints, John the Baptist, and the English Kings Edmund the Martyr and Edward the Confessor. Richard was an avid patron of the arts and collector of paintings.

In Medieval churches, the altar was directly behind the priest for the entirety of the mass, which made it the spot where every member of the congregation looked for the entire service; however, the altar was not generally an architectural feature built into the church, but something placed in later, often paid for by powerful patrons of the church. The altar piece in such a situation was a panel painting, a piece of art made on wood, usually depicting Christ, the Virgin Mary, or the patron saints of the town or church.

International Gothic was the fullest development of Gothic art, beginning in Bohemia and then spreading throughout Western Europe thanks to royal marriages and the hiring of foreign artists. The Wilton Diptych is one of the chief surviving examples of the International Gothic style, and shows the signature elements of the genre, including prominent placement of saints and the Virgin Mary in close proximity to a monarch.

Illuminated manuscripts were widely created throughout medieval Europe by a variety of religious groups, especially used with liturgical texts. This work, the Golden Haggadah, was produced for the Jewish community in Spain as a guide for the liturgy for a Passover seder. Considering the wide amounts of illiteracy in medieval Europe, containing detailed images of the story written in the manuscript allowed the entire community to understand what was contained in the work.

Image is in the public domain, accessed through Wikipedia Media Commons: https://commons.wikimedia.org/wiki/File:Enluminure_Sefarade,_Haggadah_a.jpg

The Golden Haggadah is an illustrated manuscript, as are The Lindisfarne Gospels. While separated by hundreds of miles and about 600 years, and made for two different religious traditions, each piece of art served a similar function. While presenting a religious text, each work also provides a great amount of illustrations which enhance and relate to the written text.

Image is in the public domain, accessed through Wikipedia Media Commons: https://commons.wikimedia.org/wiki/File:Enluminure_Sefarade,_Haggadah_a.jpg

The figures in this work of art, the Golden Hagganah, are representational, but still largely rough and lacking in perspective, although the work is embossed with fine detail and rich golden color. This manner of drawing and detail is highly characteristic of Gothic art, the predominant style of art in Western Europe from roughly 800 to 1350 CE. Additionally, this work of art is an illuminated manuscript, which was one of the most common forms of art in the middle ages.

Image is in the public domain, accessed through Wikipedia Media Commons: https://commons.wikimedia.org/wiki/File:Enluminure_Sefarade,_Haggadah_a.jpg