An extrapolation is kind of like an educated guess or a hypothesis. When you make an extrapolation, you take facts and observations about a present or known situation and use them to make a prediction about what might eventually happen.
Extrapolation comes from the word extra, meaning “outside,” and a shortened form of the word interpolation. Interpolation might sound like a made-up word, but it’s not. An interpolation is an insertion between two points. So an extrapolation is an insertion outside any existing points. If you know something about Monday and Tuesday, you might be able to make an extrapolation about Wednesday.