Technically all single filament lines are "mono" meaning single filament or 1 strand,i.e.; "monofilament" line. Braid is multiple filaments, each strand made up of several filaments then each strand is spooled onto a spindle or a single spindle can have more then 1 strand, the spindle attached to a carrier that can also multiple spindles, usually 4 carriers to 8 carriers. Braid is made up of hundreds of tiny filaments twisted and braided into a line.
To distinguish between monofilament lines the line companies started marking Nylon line as monofilament and Nylon line with another polymer like polyester or another type of Nylon blended as copolymer line. Easy to keep seperate until fluorocarbon line hits the market. FC is more expensive to make so it needs it's own identity although it is a monofilament line made from a polymer.
In the 80's every line maker offered copolymer line, Stren, Trilene, Ande, Maxima, P-Line with names like Silver a Thread, Ultra Green, CXX, etc. The copolymer blends offered softer, harder, stronger monofilament line as advertisements stated. Softer line with less memory being promoted for spinning reels, harder more abrasion resistant for baitcasting reels, etc, etc.
What to do with FC blended line or blended copolymer line with FC co extruded jackets?
FC was brittle with poor knot strength and expensive to make so the line folks started to blend FC with polyuerathane or polyester like they did with Nylon and gave the blends new names or called it 100% FC, all marketed as FC line. Yo-Zuri comes out with the 1st co-extruded Line with copolymer core and FC jacket marketing this new line type as "Hybrid" because it is a hybrid monofilament line. Yo-Zuri coextrusion process ends up with a larger diameter line and they realize the marketing advantage of under rating the line label strength to eliminate the problem plaguing the FC line market, poor knot strength and it works. Bass anglers adopt the hybrid as thick line vs thin line.
Sorry for the long winded rant.
Tom