Light describes and defines the general build and size of a created character in Brink, and is assigned through the Character Customization menu. A light character is only be able to wield light weapons (SMGs and Light Rifles as primaries and pistols for secondaries) and will also start with the lowest base health, but will be more agile than a character of a medium or heavy build.
This means that light characters can run faster, jump higher, and be able to execute parkour moves over objects slightly above head level. Light body types are also the only characters that can perform a wall hop, allowing them to reach to places that other body types cannot. The Light body type is not available until level 7.