Reputation

Reputation is a stat used among different NPCs. Increasing one's reputation with said NPCs will increase a player's access to their wares or services.

Cryptarch
Having Master Rahool decode Engrams will gain you skill points, which will increase his rank. At higher rank levels, he will sell more rare engrams to the player.

Vanguards
Completing faction missions for the Vanguards while on Patrol, or completing Vangaurd bounties, will earn Vanguard reputation.

Factions
The player can increase reputation with one of the factions by completing faction missions while on Patrol.