ROM Image
A ROM image, or ROM file, is a computer file which contains a copy of the data from a Read-Only Memory chip, often from a video game cartridge, a computer's firmware, or from an arcade game's main board. The term is frequently used in the context of emulation, whereby older games or computer firmware are copied to ROM files on modern computers and can, using a piece of software known as an emulator, be run on a computer.
ROMs can be copied from the read-only memory chips found in cartridge-based games and many arcade machines using a dedicated device in a process known as dumping.
- Source: Wikipedia - ROM image
Headered ROM
Usually, cartridges have multiple memory chips inside. When dumped, each memory chip is saved in the computer as one file, but most non-arcade emulators require the ROM images to be joined in a single file. A header needs to be added to the single file with information about how the multiple chips in the cartridge are associated logically. Emulators need such information in order to correctly simulate how the real machine would run the cartridge.
Most emulators can only run ROMs with headers, but unheadered ROMs exist for archival purposes.
Examples of additional information given by headers: size and location of each ROM, region, language, name of the game, version, mapper, byte order (big endian, little endian, interleaved), system type (arcade or home), presence of additional hardware in the cartridge.
Firmware
In electronic systems and computing, firmware is a specific class of computer software that provides the low-level control for the device's specific hardware. Firmware can either provide a standardized operating environment for the device's more complex software (allowing more hardware-independence), or, for less complex devices, act as the device's complete operating system, performing all control, monitoring and data manipulation functions. Typical examples of devices containing firmware are embedded systems, consumer appliances, computers, computer peripherals, and others. Almost all electronic devices beyond the simplest contain some firmware.
- Source: Wikipedia - Firmware