SharePoint is a web-based, collaborative platform that integrates with Microsoft Office.
A SharePoint Team Site is a web site that provides a central storage and collaboration space for documents, information, and ideas. These team sites are for internal use only and are built according to the organizational structure.
A project site or O365 Group is a collaboration space with a shared inbox, calendar and document library to help coordinate projects, schedules, discuss ideas and store documents. These can be accessed by external users such as a vendor or volunteer.