Reputation
From Kerbal Space Program Wiki
Reputation is a measure to determine the player's success rate at contracts. It can be gained by completing them and getting Kerbals safely back to Kerbin. Failing a contract or losing Kerbals reduces the reputation. It appears that your reputation changes the prestige of available contracts.
References
- First Contract Playthrough by Miguel (Maxmaps) uploaded on the official Kerbal Space Program channel