They use the term "giant saturation magnetization" to describe an iron nitride magnet that they made. The saturation magnetization is the point where the magnetization in a material cannot increase any further. Think of it like a maximum strength of a magnet. Neodymium magnets have their saturation magnetization around 1 Tesla, and they reported that their iron nitride magnet has a saturation point at 2.68 Tesla, so it's greater. (The magnetics community likes putting words such as "giant", "colossal", and "extraordinary" in front of terms to emphasize how big something is. Especially when it comes to magnetoresistance)

BH max is a characteristic of a magnetic material. You can think of it as a kind of magnetic energy density rating, so more is better. What you linked to showed that the iron nitride magnet they made had a BH max similar to a neodymium magnet.

Also, I love the name "Minnealloy". Very Minnesotan.