"Delta Rune" is an anagram of "Undertale."
The Delta Rune bears a resemblance to the royal crest of the Zelda series, both with three triangles and a winged figure.
The prophecy states that when an angel appears, the underground will be empty. This hints at the two main routes to beat the game, in which Asriel Dreemurr may destroy the barrier and free all monsters, or Chara may reawaken through the protagonist and kill all monsters.
"Delta Rune" may mean several things.
Delta is the fourth letter of the Greek alphabet, also known as "Δ". It reflects the triangles on the emblem.
"Rune" revolves around the meaning of magic, mystery, or spells, as the monsters mostly revolve around magic.

Okay enough shit, for the sake of it,
You've been gnomed.