In the real world, "optical" refers to vision, or the ability to see. In the computer world, however, "optical" refers to lasers, which can "see" and read data on optical discs. These discs include CDs and DVDs, which are made up of millions of small bumps and dips. Optical drives have lasers that read these bumps and dips as ones and zeros, which the computer can understand.
Some common types of optical drives include CD-ROM, CD-RW, DVD-ROM, DVD-RW, and Blu-ray drives. CD and DVD writers, such as CD-R and DVD-R drives use a laser to both read and write data on the discs. The laser used for writing the data is much more powerful than the laser that reads the data, as it "burns" the bumps and dips into the disc. While optical drives can spin discs at very high speeds, they are still significantly slower than hard drives, which store data magnetically. However, because optical media is inexpensive and removable, it is the most common format used for distributing computer software.