Malt Extract:
Malt Extract is the concentrated sugars extracted from malted barley. It is sold in both the liquid and powdered forms. The syrups are approximately 20 percent water, so 4 pounds of dry Malt Extract (DME) is roughly equal to 5 pounds of Malt Extract syrup. Malt Extract is available in both the Hopped and Unhopped varieties. Munton & Fison, Alexanders, Coopers, Edme and Premier are all good brands. Screen the ingredients to avoid corn sugar.
Using Unhopped means adding 1-2 ounces of Hops during the boil for bittering and flavor. Hops may also be added to the Hopped Extracts towards the end of the boil for more Hop character in the final beer.
A rule of thumb is 1 pound of malt extract per gallon of water for a light bodied beer. One and a half pounds per gallon produces a rich full bodied beer. Malt extract is available in Pale, Amber and Dark varieties, and can be mixed depending on the style of beer desired.
Malt Extract is what makes first time brewing simple. When the brewer starts extracting the malt sugars from the grain himself, All-Grain Brewing, then the brewer has found one half of the complex heart of brewing. The other half is the Yeast.