A decision list is a series of if-else rules, ordered by priority, used for classification or other decisions. Each rule in a decision list checks a condition and, if true, returns a certain class or outcome, and the list is structured so that the first matching rule is applied. For example, a simplified decision list might look like: “if text contains ‘$$$’ then class = spam; else if text contains ‘prize’ then class = spam; else class = not spam”. Decision lists are a human-interpretable model as they explicitly lay out the reasoning. They are related to rule-based learners and can be seen as a degenerate form of decision tree (essentially a tree that’s one long branch). Learning decision lists involves finding a good set of rules and ordering them by some criterion (like information gain or error reduction).