User accounts/profiles store user identify and preference information. Even when users are defined in external directory systems like Active Directory or LDAP, a Traction profile is created for each user to store the user's preferences.
Projects are spaces into which Articles, Comments, and Files can be published. Each Project has an Access Control List (ACL) that governs what each User is allowed to do inside that Project (the user's Permissions).
Articles are pieces of text, HTML, or metadata that can be published into Projects.
Labels are categories that can be applied to Articles. Each Project can have its own Labels. Labels from any Project can be placed on any Article in any Project. Labels provide a convenient way to gather and organize Articles. Labels in Traction are used for describing content, expressing status and priority, indicating where Articles should appear in the interface, and for modeling taxonomies.
Attachments are files that are connected to Articles, much like email attachments.
Shared Files are files or directories (folders of files and folders) that are connected either to Articles or Projects. In Traction, Attachments and Shared Files can be versioned and accessed via WebDAV (Web Folders on Windows).