JSLint and the popular alternatives JSHint and ESLint are brilliant tools that make your code more consistent. But sometimes it's hard to understand exactly what they're asking you to change. JSLint goes so far as to be proud of the fact that it will "hurt your feelings".
This page lists all of the options available to you when configuring your tool of choice and attempts to explain exactly what each option does. If you were searching for explanations of error messages you can have a look over here instead.