Typical Wikipedia error. Several things "hold" the cartridge in the barrel -- like the sides of the chamber, where "chamber" is usually a part of the barrel. The back end of the cartridge is "held in place" by the breechblock. The breech face is the part of the block that makes contact with the back of the cartridge.
Edit:
Rather than just be a smarta$$, and since I can edit Wikipedia, I tried to fix the definition there.
All of us need to sign on to wikipedia as editors, there is a lot of technical error there about firearms. I tried to fix the *benchrest* and *rail gun* entries, but they got started in a way that made this difficult. I'm not yet brave enough to throw everything out & start over -- yet. That's what a lot of entries really need, though.
For example, the "precision" versus "accuracy" split early on in the "benchrest" entry sets up an organizational structure that makes adding rimfire & long range BR difficult. It's a useful distinction, but shouldn't be the primary lead in to "Benchrest."
Bear in mind that Wikipedia likes references. To do a good job (by them), just telling the truth isn't enough. Gotta get references, which I think is what stops a lot of us.
Charles