Command buffer
A list of GPU commands recorded ahead of time on the CPU and then submitted to the graphics queue in bulk, rather than issued one call at a time.
Old-school OpenGL was "immediate mode": each call told the driver to do something right away, which tied rendering to a single thread and baked hidden overhead into every call. Vulkan, Direct3D 12 and Metal instead let you record draw calls and state changes into a buffer (D3D calls it a command list) and hand it over once it's complete.
Because recording and submission are separate, several threads can build their own buffers in parallel — a prerequisite for feeding a modern GPU. Buffers can be reused across frames when their contents don't change, and GPU instancing cuts how many commands need recording in the first place.