A stored-program computer keeps its instructions in memory instead of wiring the logic into the machine itself. That design lets the same hardware run many different programs, because changing behavior is mostly a matter of loading new code. Modern laptops, servers, phones, and routers all use this model.
This matters in cyber security because if code lives in writable memory, attackers may try to alter what the system executes. Malware, shellcode injection, and memory-corruption exploits all depend on the idea that instructions can be placed, copied, or modified in memory. Defenders build controls around the same property: code signing, non-executable memory, address-space randomization, sandboxing, and secure boot all aim to make it harder for hostile instructions to run. In a stored-program machine, protecting memory is often as important as protecting the disk or network.