kdump is a reliable kernel crash-dumping mechanism that utilizes the kexec software. The crash dumps are captured from the context of a freshly booted kernel.
kdump is a service that creates crash dumps when there is a kernel crash. It uses kexec(8) to boot into a secondary kernel (known as a capture kernel).
A 'kernel crash dump' refers to a portion of the contents of volatile memory (RAM) that is copied to disk whenever the execution of the kernel is disrupted.