A CD-ROM, or Compact Disc Read-Only Memory, is a type of optical disc used to store digital data. It can hold a significant amount of information, typically around 700 megabytes, making it suitable for software, games, and multimedia content. CD-ROMs are read by a laser in a CD drive, which interprets the data encoded on the disc. Unlike writable discs, CD-ROMs cannot be modified or erased after they are created. This makes them ideal for distributing software and other content that should remain unchanged. They were widely used in the 1990s and early 2000s before the rise of DVDs and USB flash drives.