Media, in the computer world, refers to various types of data storage. For example, hard drives, CDs, DVDs, and USB drives are all different types of media. Optical media refers to discs that are read by a laser. This includes CD-ROMs, DVD-ROMs, and all the variations of the two formats -- CD-R, CD-RW, DVD-R, DVD+R, Blu-ray, and many others.
Optical media typically does not have as fast of a seek time as hard drives (the time it takes to access information on different parts of the disk), but it has many other advantages. Because optical discs are not based on magnetic charges like hard drives are, the discs are less likely to lose their data and have a longer shelf life -- around seven times longer than magnetic media. The discs are also more durable than hard drives and are much cheaper to produce, making them great for backups and for transferring small amounts of data between different computers.