Recovery is the rate at which Endurance is replenished over time for players and critters. A higher Recovery rate increases the amount of Endurance regained at each tick, while a lowered Recovery has the opposite effect.
Recovery is based on percentages, not flat numbers. Thus, raising your maximum endurance through accolades and set bonuses will also slightly improve the amount of recovery gained each tick.
More information can be found in the Endurance article.
Currently the maximum Recovery % is 8.34%.