A repository is a versioned collection of files together with their full history. Git calls it a repo, Perforce calls the server-side storage a depot, and USourceControl calls it a project.
The naming difference is not cosmetic. In Git, a repository is the unit of cloning, branching, and access control all at once, which is why software teams end up with many small repositories. In game development the natural unit is the game: one .uproject, one team, one set of permissions. Calling it a project rather than a repository matches how the people using it already think, which matters when half your users are artists rather than engineers.
Structurally the concepts line up. A USourceControl project holds files, full version history, membership and roles, and settings such as the exclusion list. Where it differs from a Git repository is that there is no local clone carrying all history: your machine holds the current state, and history lives on the server, retrieved on demand. On a project where history measures in terabytes, that difference is the point.