...Which one?
While rules for using them are being updated, and they still effectively exist, Land-Air 'Mechs (LAMs) have simply fallen out of favor and fashion in both real-world (game) and universe. Not to mention the Nova Cats found them such abomination that they destroyed the factories...the art wasn't updated for Project Phoenix. Fortunately, the new license eliminates the necessity of redesigning them, so they've always looked like Gerwalk VF-1s.
Fluff is essentially all the little details that make a story complete (in BattleTech for example, notable design flaws in 'Mechs, notable pilots, various successes and failures of certain weapon systems, etc). Also generally used to refer to the "behind-the-scenes" fiction of a given universe.
In Macross, a VF-1 Valkyrie is an aerospace fighter that can transform into a giant robot. This is all we need to know. But if you look into it a little bit, you can find the manufacturer who made the engines, and their exact output specifications. That is the fluff - it makes the VF-1 a little more well-established and "real". The concept of the DYRL OAV can be considered fluff (it's an otherwise inconsequential movie made within the universe!). If we knew Capt. Global's eating habits, they'd be fluff.
Fluff is also a sticky, delicious marshmallow-flavored spread invented in Somerville, MA.