Hallowed Be Thy Name is related to the seasonal world event Hallow's End. If you complete this achievement you will be rewarded with the title <The Hallowed>. Completing this achievement is criteria for the meta achievement What a Long, Strange Trip It's Been.
"Hallowed be thy name" is a line from the "Lord's Prayer" in Christianity.
"Hallowed Be Thy Name" is also the name of a song by the British Heavy Metal band Iron Maiden
The Random House dictionary defines "hallowed" as "holy; venerated; sacred". The day after Halloween (which literally means "All Hallow's Eve") is All Hallows Day (or All Saint's Day). In most Christian churches it is a day to remember the saints, and in many denominations it is a general commemoration of the dead, although its origins predate Christianity.