From Lexicanum

Mega Armour is used by the Orks and is a suit of massively thick armour with heavy plates over an already powerful exoskeleton. The weight (a ton or more^1a) and complexity makes it difficult to move in although it protects against most attacks, and includes a Shoota and Power Claw. The Shoota may be upgraded to a Kombi-Shoota and/or Kustom Shoota. Because of the extra weight, even solid, flat ground is treated as difficult terrain. They may not be armed with Jump packs, Bikes, Infiltration, Bioniks, Frag Stikkbombz, Krak Stikkbombz or Tankbusta bombz, however they may be equipped with Mega Boostas, powered boosters to allow them to compensate for their slow progress.

Sources

• Warhammer 40,000: Wargear
• ¹ Codex: Orks (4th Edition)

^a p.39

See also

• Armour
• Mega Boosta