Camelot: This one you've probably heard of; it's famous for being the castle where the legendary King Arthur and his Knights of the Round Table lived. There are lots of legends about Arthur, written in several languages, and they give different details about Camelot. Maybe the most famous of the books about Arthur and Camelot is Thomas Malory's Le Morte d'Arthur (The Death of Arthur), written in the fifteenth century.
Lancelot: Another big player in Arthurian legend. One of the most famous of Arthur's knights, he causes a bunch of trouble by sleeping with Queen Guinevere. Like we see in this poem, Lancelot seems to be trouble around the ladies. Again, he's a major character in Malory's Morte d'Arthur. That book tells one version of the story of Elaine of Astolat, who falls in love with Lancelot and then dies when he breaks her heart. If you want more info about Arthurian legend, we've posted some links in our "Best of the Web" section.
Red-Cross Knight: Red-cross Knight is one of the heroes of Edmund Spenser's epic poem The Faerie Queene. "The Lady of Shalott" doesn't mention that character directly but it does talk about how Lancelot has a picture of "a red-cross knight" on his shield (line 78). Tennyson's readers would definitely have gotten the reference to Spenser. They would also have known that a red cross is the symbol of St. George, the patron saint of England. So this quick shout-out to the red-cross knight does a lot of work. It connects Lancelot with another great work of literature, but also with the idea of chivalry, bravery, and the history and glory of England.
"Tirra-Lirra" : This weird little bit of a song is one of only two lines that Lancelot speaks in the whole poem. It's a reference to a song from Shakespeare's The Winter's Tale (Act 4, Scene 3) where one of the characters sings a song about "The lark, that tirra-lirra chants."