Tip-top means excellent, as good as it can be. It is a cheerful, slightly old-fashioned word, and it is much more common in British English than American. You hear it most in two places. First, about condition or health: 'in tip-top condition', 'in tip-top shape' — a car that runs perfectly, a garden with nothing out of place, a runner who is fully fit. Second, as a quick friendly answer: 'How are you?' 'Tip-top, thanks!' The feeling of the word matters as much as the meaning. Tip-top is warm and light. It is the kind of thing a grandfather says, or a shopkeeper, or a coach patting you on the back. In writing it appears in advertising and in friendly speech, almost never in serious or formal writing — a report would say 'in excellent condition', not 'tip-top'. Younger speakers use it less, and when they do it is often half-joking, with a wink at how old-fashioned it sounds. That is not a problem; it just means the word carries a bit of personality with it. Grammatically it usually sits before a noun (tip-top condition, tip-top service) or stands alone as a reply. The picture inside the word is simple: the tip is the very end of something and the top is the highest point, so tip-top is the highest point of the highest point — you cannot go further up.