Marks of Valor are a type of currency used to purchase PvP gear. As of Update 25, they replaced Marks of Strategy, Marks of Tactics, and, in most cases, Influence.
All sets of PvP gear (Tiers 1-5) can be purchased using Marks of Valor. Players can win these marks in lockboxes, and through Arena PVP and Legends PVP.
Marks of valor can also be used to buy Synthetic Mods - which can be used on PvE gear.
Currently, the maximum Marks of Valor that can be obtained is 6,250