ROM, or read-only memory, is non-volatile storage used to hold code that is available as soon as a machine powers on. In practice, it often contains firmware, boot code, or recovery routines that run before the operating system starts. Because it is designed to be hard to change, ROM provides a trusted starting point for the device.
In cyber security, ROM matters because code placed there can influence the entire startup chain. Attackers may try to replace, abuse, or bypass firmware stored in ROM or ROM-like regions to gain persistence or hide from normal system tools. Defenders rely on ROM-based code for secure boot, hardware initialization, and rescue features, but they also need verification and update controls, since flaws in early boot code are difficult to detect and remove.