"Fast Flight" is a brand name. It's also used generically to describe most any "high performance" material. The name is owned by Brownell, but ironically the material was invented by the founders of BCY.
Flemish Twist is one of the ways a string is constructed. You put individual strands into 2 or 3 bundles and twist the ends back into the body of the string to form the loops.
Endless or continuous loop uses one (you can use 2 or 3 also) strand wrapped round and round on a jig. The loops are formed by serving.
B-50 is also a trade name, and also used generically for the two polyester (usually referred to as "Dacron") string materials on the market--B-50 (brownell) and B-55 (BCY).
There are three basic types of string material:
100% HMPE (high modulus polyethylene) or UHMWPE (ultra high molecular weight polyethylene).
These include materials like Dynaflight '97, Formula 8125G, and 8190 Universal.
HMPE/Vectran blends. These include materials like 450+, 452X, and Trophy. Vectran is added to improve stability, but hinders speed just a tad, at least with wheel bows. It also has a tendency to fuzz up quicker.
Polyester; B-55 and B-50.
There are different grades of HMPE. Original "Fast Flight" was SK65 Dyneema--lots of stretch and creep compared to today's top materials, but it revolutionized bowstrings in it's day. Dynaflight '97 is SK75 Dyneema--it was top dog for many years, and is still a very popular material. 8190 is SK90 Dyneema--the strongest, most durable HMPE material on the market.
Dyneema is a trade name for HMPE, and considered to be one of the best. There are cheaper imitations that are used in some materials, but not BCY materials. The higher the SK number, the higher the quality and grade of Dyneema.
Hope this helps.
Chad