Righto is a small spoken word that means “yes, okay, I’ll do that” or “that’s fine with me.” Someone says “Shall we leave at six?” and you say “Righto.” It is friendly, a little old-fashioned, and very much British, Australian, or New Zealand — you will almost never hear it from an American. It is not a full claim that something is correct; it is more like a cheerful nod. Though actually, the tone can also mean “that’s enough, I understand, let’s move on,” a bit like “all right then.” You may see righto, right-oh, or right oh. It is informal. Do not put it in a school essay unless you are copying how someone spoke.