An MPEG is an acronym meaning "medium-power electric gun". This denotes AEG's of good quality and relatively low price. MPEG's can be considered the most popular and common airsoft guns around.
As mentioned before, MPEG's are usually guns of stock quality, not shabby but little lacking.
MPEG's are typically low in price, from as low as $75 to as high as $200.
Actual performance of MPEG's is suitable for close-medium range battle. FPS is somewhere between the 300 and 400 FPS range, and depending on fps, a .25 or .28 gram BB's are best for use in an MPEG. .20s are mean't to be used in weaker guns such as non modified AEPs that fire in the 200-230 range. For CQB fields it is best to use .20s because they are cheaper, elite force stocks the cheapest and minimal quality bbs. They are not for regular field usage as they have tons of bubbles in them which cause them to fly in all kinds of stupid directions. Depending on your fps, you can use even cheaper bbs than elite force, .12s can be used for extremely close quarters play due to the size of the springers that use them, lightness and low fps. The best bbs for a low price are G&G .25s and .28s which cut through wind because of their weight, hit targets slightly faster due to their storage of force in inertia rather than velocity.
MPEG's are the most popular airsoft rifles on the market. As a result, they are manufactured by nearly everyone, but high-profile manufacturers include names such as: -Tokyo Marui -Echo1 -Umarex -Jing Gong (JG)