CDs were once the most popular form of physical audio storage. Now it's a battle to burn them.
For those who grew up with a player in their car stereo, the CD will always be a nostalgic piece. From an audio engineering standpoint, the CD is a beautifully simple method of transporting high quality audio—reliably and universally—to any system.
For a detailed history of the CD: https://en.wikipedia.org/wiki/Compact_disc
*I'll eventually write a "TL;DR" version of that page.
Audio vs. Data
CDs can store audio in two different formats: CD-DA (CD-Digital Audio) or Data CD (think MP3 or WAVE). In CD-DA format, a CD is playable on any system, regardless of age, brand, or type (PC, portable, in-dash, hi-fi). In "Data CD" format, a CD is generally only usable on some players.
CD-DA is the original Red Book format. It is universally understood by all players and is able to be "ripped" by personal computers. This format is burned as 2-channel, 16-bit audio at 44.1 kilosamples per second (maximum representable frequency of 22.05 kHz). There are inherent error-correction methods in this format and it is the most efficient means of using physical space on the CD.
A Data CD is a CD which is used to store files of any type—not just audio. Several types of Data CDs are available, namely the CD-ROM (Read-Only Memory), CD-RW (Re-Writeable), and CD-R (Recordable). In terms of audio, WAVE, MP3, and some other formats are occasionally supported by CD players (if written correctly). Some players will even accept audio files in a directory tree, meaning one can visually organize songs by album, artist, or genre with folders.
Created by HP in 2004, LightScribe was a technology which allowed consumers to create customized, monochrome graphics on the label side of their CDs, and it did so with the same drive that wrote the data.
Here's an interesting video by Technology Connections on YouTube which details LightScribe's history: