In general, on GitHub, 1 repository = 1 project. For example: https://github.com/spring-projects/spring-boot . But it isn't a hard rule.
1 repository = many projects. For example: https://github.com/donhuvy/java_examples
1 projects = many repositories. For example: https://github.com/zendframework/zendframework (1 project named Zend Framework 3 has 61 + 1 = 62 repositories, don't believe? let count Zend Frameworks' modules + main repository)
I totally agree with @Brandon Ibbotson's comment:
A GitHub repository is just a "directory" where folders and files can exist.