Teams

Teams group members' access to a specific focus, e.g. a major product or application that may have sub-projects. As of a recent release teams have fully replaced Access Groups (which are now considered deprecated, and can no longer be managed).

Projects

Projects generally separate different services or roles within your application. For example, a web app might have different projects for it's worker processes than it uses for its web processes. It might also split production and staging environments into different projects.