"The world of big robots both animated and not. Often associated with Anime/Manga but not tied to that genre.
Mecha, also known as meka or mechs, are walking vehicles controlled by a pilot, often appearing in anime, science fiction, or other genres involving a fantastic or futuristic element. Mecha are generally, though not necessarily, bipedal, with arms, hands, and fingers capable of grasping objects. A mecha that approximates the shape of a human body allows the use of martial arts movements and swordsmanship, ceremonial acts of honor, saluting, and other human mannerisms that cannot be performed using a tank or airplane.
In most fiction in which they appear, mecha are war machines: essentially armored fighting vehicles with legs instead of treads or wheels. Some stories, such as the manga Patlabor and American miniature games BattleTech, also encompass mecha used for civilian purposes such as heavy construction work, police functions or firefighting.
Some science fiction universes posit that mecha are the primary means of combat, with conflicts sometimes being decided through gladiatorial matches. Others represent mecha as one component of an integrated military force, supported by and fighting alongside tanks, fighter aircraft, and infantry, functioning as a mechanical cavalry. The applications often highlight the theoretical usefulness of such a device, combining a tank's resilience and fire power with infantry's ability to cross unstable terrain. In other cases they are demonstrated with a greater versatility in armament, such as in the Armored Core series of video games where mecha can utilize their hands to carry a wide range of armament in the same manner as a person albeit on a much larger scale.
The distinction between true mecha and their smaller cousins (and likely progenitors), the powered armor suits, is blurred; according to one definition, a mecha is piloted while a powered armor is worn. Anything large enough to have a cockpit where the pilot is seated is generally considered a mecha.
Rarely, mecha has been used in a fantasy convention, most notably in the anime series Aura Battler Dunbine, The Vision of Escaflowne and Maze. In those cases, the mecha designs are usually based on some alternative or 'lost' science-fiction technology from ancient times."
Source: Wikipedia, "Mecha", available under the CC-BY-SA License.