Runes in Elden Ring, analogous to the Souls of previous FromSoftware titles, act as the player's EXP and currency for Merchants. You will drop any runes in your possession at the site of your death. If you die again before reclaiming those runes, they will be lost forever. The compass at the top of the screen indicates the direction of the lost runes.
Runes are primarily pieces of the Elden Ring which were separated during the Shattering. The currency we collect are tiny particulate shards, so small that they are basically worthless on their own. Rune Arcs are larger pieces from a specific and important part of the Ring. Great Elden Ring Runes are massive chunks that were knocked out of the Ring and then claimed by Demigods.
Enemies are the main source of runes. Defeating the inhabitants of the Lands Between will award you both runes and Items.
Occasionally enemies have golden glowing eyes, indicating that they will drop five times their usual amount of runes.
Bosses are a substantial source of runes. Conquering the strongest of foes merits a bounty of runes.
Remembrances drop from certain bosses upon defeat which can be consumed for runes or exchanged for powerful items.
During Multiplayer Co-op, the Host receives 75% of the boss's rune reward and Cooperators receive 25%.
Golden Rune Consumables are a reliable source of runes. Like all items, they are not lost on death so you can store them up and use them when you need a few more runes.