Part of what makes GitHub great for collaborative software projects is its support for linking disparate pieces of information together. Some of this happens automatically, such as when you create a pull request from a series of commits on a branch. Other times, you can use the interface to manually link pull requests or projects to issues using the dropdown options.
To make it even easier to cross-link different items throughout your project, GitHub offers a shorthand syntax. For example, if you leave a comment like Duplicate of #8, GitHub will recognize that #8 is an issue and create the appropriate link for you.
An autolinked issue
Learn more about Autolinked references and URLs .