From Destinypedia, the Destiny wiki
Legendary Marks are a form of currency used to purchase Legendary gear. They were introduced in The Taken King as a replacement for Vanguard and Crucible marks. Like glimmer, marks are shared across all three characters. While there is no limit to how many marks per week a player can collect, the cap is at 200 marks.
Legendary marks can be acquired the following ways:
Legendary marks can be spent on: