Definition: In computer science, a "pretreatment" or "preprocessing" is an operation that transforms or normalizes input data before it is used in machine learning algorithms. This process can include things like normalization (scaling values between 0 and 1), feature selection, dimensionality reduction, etc. For example, if we have a dataset of images, some might want to normalize the pixel intensities so that they all fall within a certain range (e.g., 0-255).