Pretty much everything programmers do is create unproven algorithms. Hopefully at least some of them are correct. A heuristic is a problem-solving approach that has a chance of failure. So say you need a pretty fast dictionary, and you can take a relaxed attitude to correctness. You can take a hash of the words of your dictionary, and then as you are filtering some dataset, you can always say in a short time whether a value is definitely not in your dictionary, but your positive solutions have a percent chance of being incorrect (e.g. a hash collision). The idea is generally to make a problem tractable that would otherwise be computationally difficult or impossible. I'm not sure if that quite answers your question.