Your reputation. Your Social Credit results from anything that you or others have made public about you, primarily as a result of online profiles, including Facebook, Twitter, etc., but also including your offline reputation.
Photos of you posted online and/or word-of-mouth stories about you can have a positive or negative impact on your social credit.
If you have a seedy reputation, you don't have much social credit. If you're an upstanding citizen or are a leader in your peer group, you have a lot of social credit.
Jason has got to be the most popular person in school. That guy has some serious social cred.
The CEO is worried about his social credit after that story in the newspaper about his DUI.