Windows, bottles, vehicle windshields, etc, but not pottery/ceramic vases, crates (wood/plastic), and other non-glass breakable objects.
Beakable glass was made to allow the players to break windows to pass through or simply be able fire or throw things through the window and simulate how real windows work.
Early games allowed to break windows entirely with a single shot or a few shots, but without a realistic degradation and breaking effect, later when the technology was more evolved, players could make holes in a window with also more realistic physics about the simulation of the breakage of the window.
Windows in newer game can react differently when a large or small projectile hits it; for example a bullet can make a hole and pass through and if you fire more bullets around the hole the results are similar to what happens when a real window is impacted by bullets.
A rocket pass through instead of exploding on contact against the window, etc ...