Heimdall's Aett is the second of the three groups of eight runes making up the Elder Futhark, covering Hagalaz, Nauthiz, Isa, Jera, Eihwaz, Perthro, Algiz and Sowilo, the middle third of the twenty four rune row as the Kylver Stone's dividing marks lay it out. Where the first aett opens on Fehu, wealth and increase, this middle group opens on Hagalaz, hail, a sign generally read across the surviving rune poem tradition as disruptive and destructive, so the row moves from an opening group weighted toward growth and social bonds into a middle group whose early runes, hail, need and ice among them, read considerably harder, before the group closes on Sowilo, the sun, one of the row's most straightforwardly favourable signs.
R. I. Page's account of the Old English rune poem, the earliest and fullest surviving commentary on individual rune meanings even though it describes the later Anglo-Saxon futhorc rather than the Elder Futhark directly, glosses Hægl as a grain that falls from the sky and troubles the world, a reading broadly consistent with how this aett's opening sign is read across the wider tradition. The middle position of this aett within the row's three part structure has invited comment from modern rune workers about a possible movement from beginning through trial to completion across the three groups, though this reading is an interpretive layer rather than anything the Kylver Stone or the early sources state.