I'm feeling verbose. So here we go.
Dark matter: Maybe something that we'll one day make lunch boxes out of. Maybe also a rounding error. Of some sort. In some way. You haven't got the mountain-of-data yet. A lot-of-data is a good start. This doesn't mean the missing matter isn't some super-energy infused version of something we already know about. For all we know, its simply "ordinary" matter we'd otherwise already have accounted for but seen/detected in distorted ways due to some new phenomena altering our perception. So, its real as opposed to unicorn droppings[0]. But thats only a small part of the story.
Neither dark energy or matter exist as permanent fixtures, or even as just two singulars. They are placeholders while the search for the underlying phenomena continues. The moment the unaccounted matter/energy is discovered due to phenomena A, B, C, D, E, F then those two broad individual placeholders will be replaced with more detailed names, likely in honor of someone famous or otherwise noteworthy feature of the discovery, eg shape, some quantify etc. We'll go from "dark matter" to phenomena A,B,C to something1, something2, somestate3 or whatever.
People like saying dark[1] because it sounds cool, mysterious and edgy. Its the flair for the dramatic. This is fine for awhile as long as it helps. It is a mystery. But today its a big mystery and tomorrow its on someones balance sheet. There's a lot of tomorrows to allow that to happen.
Very important note: Our knowledge is not dark. Knowledge shines light over the unknown so we can see it for what it is. That is the whole point.
[0] I'm asserting for sake of argument that unicorns aren't real. Some could say that horses with a horn were hunted to extinction and we just haven't found a sample. Thats valid as well. I'd still prefer to see some evidence like a skeleton. But for now, I'll just assume for the sake of argument they don't exist and leave the real answer as homework for the interested[2].
[1] Dark. Or transparent. Maybe we are seeing through it instead. Plastic bags in water become "unaccounted for" and can visually disappear due to transparency. Some ocean creature could easily call that bag the equivalent of what we would call dark matter. Its got water in it and around it. Ordinary matter surrounded by something they don't understand. Hydrocarbons. In explaining it we'd mention the multiple processes and atoms responsible for the formation because we know how hydrocarbons are formed. And probably not just one thing. (No I'm not suggesting dark matter is hydrocarbons but I retain the option to ironically laugh if they are a form thereof).
[2] I know an 8 year old who is highly motivated to believe they're real and with enough skills at genetic manipulation she might make it happen. And apparently they eat meat. The small-hill-of-data implies we should be careful out there.