A "complete" home theater sold as a single unit or package (usually in 1 box). It consists of five or more speakers, a low frequency speaker (subwoofer), and a receiver. Some packages also include a DVD player. These are inexpensive and are a good choice for your first theater or in a secondary room and allow you to upgrade in stages to separate components. Consider them an adequate "starter home theater".
a complete surround sound system
Any of several kinds of packaged audio-for-video systems designed to create an "instant" home theater; usually inexpensive and compact. Typically includes a multi-speaker complement plus a receiver or multichannel amplifier to drive the speakers. May function as a stand-alone 5.1-channel system or may be designed to add channels to an existing stereo or other audio system.
A complete home theater system in one box (or at least sold together as a package). Consists of five or more speakers, a subwoofer, and a receiver. May also include a DVD player.
A very poor substitute for the real thing. See Home Theater above.
A "home theater in a box" (HTIB) is a common name for a relatively inexpensive integrated home entertainment package, usually including a DVD player, surround sound capability, and a radio tuner in one box. While they lack the features of a custom-assembled home theater system, HTIBs are an inexpensive (and generally space-efficient) way to take advantage of the surround sound capabilities of the DVD format. They are manufactured by most makers of consumer electronics; Bose in particular markets their integrated home theater systems especially aggressively, though other traditional manufacturers such as Sony, Philips, and Panasonic market systems that tend to be considerably cheaper.