Hallo is an old way to write hello — the same greeting, not a different word. You use it to say hi, to start a phone call, or to catch someone’s ear. English used to spell this call in several ways at once: hello, hullo, hallo, halloo. Hello won, so hallo now looks old on the page. You still meet it in old letters, old stories, and when someone is being playful and old-fashioned on purpose. Though actually, hallo was also a shout into the distance — to a person far off, or even to dogs — before it settled as a friendly hello. German Hallo is their everyday hello; that is their spelling in their language, not a special English meaning.