React: What is React 18 startTransition?

1import { startTransition } from "react";
2
3function Search() {
4  const [query, setQuery] = useState("");
5  const handleInput = (e) => {
6    setQuery(e.target.value); // urgent
7    startTransition(() => {
8      setSearchResults(filter(data, e.target.value)); // non-urgent
9    });
10  };
11}