Project contributions are historically known as sprints. A contribution day is an important part of Drupal's growth, and provides great opportunities to get involved in contributing to Drupal itself. Everyone is welcome!
You don't need to be a developer to contribute. We need: project managers, bug reporters, QA testers, people to help write documentation, etc... If you ARE a developer, but not sure where to get started, we have mentors to assist you.
Contributing can take many forms. Contributors do not have to be coders. Projects can use testing, documentation, issue triage, user experience, you name it! There are so many ways for folks to value to open source.