A DVD player connects to your television in order to allow the playback of digital versatile discs, a digital but standard-definition form of optical media used for movies and music alike. A DVD can store much more information than an audio CD or CD-ROM, but less than high-definition formats such as Blu-ray Discs.
Optical disc players are generally backwards-compatible - this means they can play earlier formats, but not later formats. Therefore, a DVD player will usually be able to play audio CDs, and potentially play MP3s that are stored on CD-ROM, but will not be able to play HD formats like Blu-ray. A DVD player may also incorporate a surround sound decoder, and some come with their own speaker system for surround sound playback.