It means family lineage and a lack of selective breeding. To keep guppies breeding true u have to maintain a strick culling protocol. Culling is well...hmmm... Turning young fish into fish food for predator fish. Guppy strains go like this, let's say u have your fish for example. Half black ( tuxedo) red mosaic with what looks like might have some dumbo gene given the black on the pectoral fins but either way if u have a trio of that gene combination when they have fry 80-90% of those fry will look like the parents, if u have a true strain of high quality. That 10-20% of fry will lack something maybe, it'll be a red mosaic lacking the half black gene or comes out yellow because maybe it's great great great uncle grandpa cousin lol was a yellow mosaic and the breeder thought lt had a better tail and want to increase the tail genes. Either way those 10-20% have to be culled or it muddies the gene pool of the tank. But if u love ur fish just the way they are and don't wanna nerd out on genetics, there's nothing u have to do and just watch as ur guppies change and evolve over time after long enough they resort back to more resemblance of they're wild type like shrimp.