The new Harry Potter title, 7th in the series, has now been announced, and for those of us who still pray "hallowed be thy name" in the Lord's Prayer, it seems to forebode a resurrecting of the term. Here's a quick definition from Wikipedia:
Hallow is a word usually used as a verb, meaning "to make holy or sacred, to sanctify or consecrate, to venerate".  However, in Harry Potter and the Deathly Hallows, the word hallows appears as a noun. In modern English, the word is used as a noun in "All Hallows' Day" or "All Saints' Day," which is the day after Hallowe'en or "All Hallows' Eve". Hallows can refer to saints, the relics of saints, or the relics of gods. One story where hallows play a crucial role is in the grail legend. In the Grail legend, the Fisher King is the guardian of the four hallows, which include the Grail itself, the serving dish/or stone, the sword/or dagger, and the spear.  Many scholars have since identified the connection of these four hallows with four treasures of the Tuatha de Danaan, which include a chalice (Grail), a baton or wand (spear), a pentacle (serving dish), and a sword.
There has been much speculation from many Harry Potter fans about whether the grail legend might play a part in the final Harry Potter book. Many Harry Potter fans have seen a connection between the four founders of Hogwarts, their relics, and the four hallows in the grail legend. It is known from the books that Godric Gryffindor's relic is a sword, Helga Hufflepuff's relic is a cup (chalice), and Salazar Slytherin's relic is a locket (pentacle), presumably leaving Rowena Ravenclaw's relic as a spear or wand. In addition, many scholars have argued that the four hallows in the Grail legend symbolize the four natural elements (earth, fire, water, and air). J. K. Rowling has explicitly stated that the four Hogwarts founders represent the four natural elements, solidifying the connection between the four founders and the four hallows in the Grail legend. It is also known that Harry Potter must find four horcruxes, and that Voldemort wanted a hallow, or relic, from each of the four founders.
So, apparently one can exegete Harry Potter.