Ether Seals are magical seals that are placed by the Mursaat in key places (gateways, doors, etc.) to help guard them. Ether Seals themselves are usually guarded by Mursaat or Jade Armor/Jade Bows. When found on a gateway or door, destroying the Seal will open the way through. They are also sometimes found on Mursaat Towers, which (when powered by a Seal) constantly drain energy, deal damage, and strip enchantments inside the glowing ring around them. Destroying the Seal in this case will remove the tower's effects.
Ether Seals have a moderately large amount of health and their health regeneration makes them quite difficult to kill. Since they cannot move, Area of Effect spells are particularly effective.
Tests have shown that the Ether Seals possess the same advantage as Tyrian bosses: Natural resistance. This means that hexes and conditions only last half their normal duration. In combination with their heavy health regeneration it would seem Ether Seals have all the advantages of a boss without the associated Morale Boost from killing them.
Both of an Ether Seal's spells cause Exhaustion. With a tank and good healer or two, it's possible to simply wait and let the seal reach max exhaustion, thus rendering it harmless. Equinox will speed up the process.
Ether Seals will only use Glyph of Concentration when Dazed.