Harpy is a Grimoire card from the original Destiny (Destiny 1), found under Enemies → Vex. 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
The fastest and most mobile Vex, the Harpy is an airborne unit often deployed in flocks on patrols and scouting missions. They must stop and stabilize before attacking.
Grimoire text written by Bungie, shown as it appears in the Destiny 1 game files.