The term descends from common Germanic religion, continuing a Proto-Germanic *har(u)gaz, attested in Old English word hearg (plural heargas, surviving as the placename Harrow in England and as Harge in Sweden) and Old High German word haruc (plural harugâ). A possible cognate in Celtic cairn, ultimately from the same root as horn.
Jacob Grimm in his Teutonic Mythology lists glosses of haruc translating fanum, delubrum "shrine, sanctuary", lucus, nemus "grove, temenos''". The gloss nemus plantavit: forst flanzôta, edo haruc, edo wih. "he planted a wood, or haruc or wih (Diut. 1, 492) suggesting that haruc like wih originally referred to a sacred grove. The Lex Ripuaria has preserved, evidently from heathen times, harahus "harrow-house" to designate a place of judgment, which was originally a wood. Anglo-Saxon has heargtræf "harrow-dwelling" (Beowulf 349) and æt hearge "at harrow" (Kemble 1.282). The Eddaic poem Völuspá speaks of the Æsir as builders of hörg ok hof "hörgr and temple".
A possible use of the hörgr during a sacrifice would be to place upon it a bowl of the blood of an animal sacrificed to a Norse deity (e.g. a goat for Thor, a sow for Freyja, a boar for Freyr), then dipping a bundle of fir twigs into it and waving the bundle in the form of the "hammer-sign" to spatter the participants with the blood. This would consecrate the attendees to the ceremony, such as a wedding.
Like Judeo-Christian and other traditions, the Norse religion vested great spiritual significance in blood. The Eddaic poem Hyndluljóð speaks of a hörgr built to Freyja by Ottar: hörg hann mér gerði hlaðinn steinum; nú er grjót þat at gleri orðit; rauð hann í nýju nauta blóði "he built me a hörgr heaped with rocks; those stones are now turned to glass; he reddened it with fresh blood of cattle". The reference to glass may indicate the burning of fires on the stones.