If a relationship is platonic, the two people care about each other, but not in a dating or sexual way. They are friends. You hear it when someone wants that to be clear: “We're close, but it's platonic.” It can sound a little careful or formal, the kind of word you use so nobody gets the wrong idea. Though actually, the word first belonged to Plato, the Greek thinker. He wrote about a love that reaches toward something beautiful and good, not toward a body. English later narrowed that big idea into this smaller everyday meaning: friends, not lovers. People still sometimes say “Platonic love” for the older, high-minded sense, with a capital P. In ordinary talk, though, platonic almost always means “not romantic, not sexual.” It does not mean the friendship is cold. It only says the heat is not that kind of heat.