Low-Frequency Effects (LFE) Channel
The low-frequency effects channel (LFE) in a home theater system is more commonly known as a subwoofer. It is a speaker specifically designed to play only the lowest frequencies of audio, from about 120 Hertz on down.
Movie mixing engineers now mix specifically to send the deepest and most demanding bass to the LFE, instead of assuming that your larger front speakers can powerfully reproduce ultra-deep bass. All surround sound systems for home theaters need an LFE.
The most common placement for a subwoofer is in a corner, where it will be louder than if you place it elsewhere in a room. This isn't, however, the most accurate place for it. For that you will need to do the "subwoofer crawl." This involved placing the subwoofer at the location of your head when you're listening to music/movies (no joke) and crawling along the walls listening for where the bass sounds best.