Tableau Prep is a tool for preparing data for analysis in Tableau. It allows users to connect to various data sources, combine and clean the data through a visual flow process. Key features include connecting to multiple data sources, using steps to filter, pivot, join and clean data, tracking changes, and applying operations to entire datasets. The document provides examples of using Tableau Prep to clean data from multiple files by adding/removing fields, standardizing date formats, handling missing values, and merging datasets.