Haldex is a Swedish company manufacturing for example the Haldex limited slip coupling used in vehicles with automatic all wheel drive systems to engage and disengage a secondary axle when needed.
Incidentally, among car fans (European mostly), a "Haldex" refers to the aforementioned differential system: its most prominent use is in all transverse engine 4x4 models of the VAG group (Audi A3 and TT, Volkswagen Golf and Passat...), making them non permanent 4x4s, unlike longitudinal engine models (Audi A4, A6, A8) which use a Torsen-like differential. However, its short reaction time (only a seventh of a wheel spin) amply makes up for its non-permanent AWD (like Torsen) setup.
Also noteworthy is that purists despise the fact that "low end" Audis equipped with the "Haldex system" bear the same name (quattro) as their "greater" brethren using the Torsen differential: true, the original Audi Quattro coupe did use a Torsen differential - but then again, it had a longitudinal engine.
Haldex Traction is a part of the Haldex Group that is responsible for the manufactoring and marketing of the Haldex AWD system.