What is emulation?
Emulation is the process of simulating the hardware of one machine on another machine so that the second machine is able to run software designed for the first machine. The most popular type of emulation is video game emulation. This is when someone plays games from NES, SNES, Genesis, etc. on their PC.

What is an emulator?
An emulator is the software that simulates the machine you wish to emulate. This program allows you to run games that is designed for another system, such as NES, SNES, Genesis, etc.

What is a ROM file?
ROM stands for Read Only Memory. They are the games you run using an emulator.

Why doesn't this ROM work with this emulator?
Certain emulators run certain ROMs better, depending on its compatibility issue with it. Try running the ROM with different emulators. If the ROM still doesn't work, it's most likely that it's corrupt (not playable).