What it means in the "real world" of this story is... Nothing. All the things it's attached to exist, but it itself, as a term, is otome game jibberjabber. It's a bit like "charm magic" in that sense.
What it means functionally, what the girls are really concerned with, is "a person who can show Cecil how to love." And with learning to love, learning to have feelings besides boredom and being able to be happy. With that comes becoming a good king whose realm isn't plunged in whatever direction his hollow search for something of interest leads. That's the impact his "fated maiden" should have on him if she's on his route.
Additionally, "a person who gets a fancy magic mark when she kisses him," but that's basically irrelevant, because that has nothing to do with fate, or the above emotional reason, and everything to do with a thing spirits can do for their contractor's partner.