Mote of Light
From Destinypedia, the Destiny wiki
A Mote of Light is an Item Guardians collect by accumulating 80,000 experience after reaching Level 40, opening loot chests in Patrol, decrypting Engrams, completing Bounties, dismantling gear, completing Crucible matches and Vanguard Strikes, or finishing a Public Event with Gold ranking. Xûr, Agent of the Nine also sells Motes for two Strange Coins apiece.
Motes of Light can also be used as a consumable as of The Taken King. Activating a Mote instantly grants 1500 XP, similar to turning in a Bounty.