When you extrapolate, you take facts you already have — about now, or about one group — and you use them to guess about later, or about a bigger group you have not measured. Scientists do this with graphs: the line goes as far as the data, then they continue it a little further and say, if this keeps going, here is where we land. Business people do it with sales; weather people do it with trends. Though actually, the further you go past the last real fact, the more the guess can go wrong. People also use it loosely in talk: don’t extrapolate from one bad day — meaning one example is not a pattern. It is a careful science word that everyday speech borrows, sometimes too freely.