Psion is a Grimoire card from the original Destiny (Destiny 1), found under Enemies → Cabal. Grimoire cards held most of the game's lore and were read on Bungie.net and in the companion app, not in the game itself.
Card text
Psions are smaller than all other Cabal morphs, and may be an unrelated species. Hyper-intelligent, fast and unpredictable, they possess strong psionic capabilities - including the ability to emit disorienting and deadly psychokinetic Arc blasts.
Grimoire text written by Bungie, shown as it appears in the Destiny 1 game files.