Based on the search results, "diff" can refer to two different things:

1. Utility diff: In computing, "diff" is a data comparison tool that computes and displays the differences between the contents of files. It is used to show the changes between two versions of the same file and can be used to compare binary files as well as text files. The output is called a "diff" or a "patch" and can be applied with the Unix program patch. There are some modifications and extensions to the diff formats that are used and understood by certain programs and in certain contexts.

2. What The Diff: "What The Diff" is an AI-powered app that reviews the diff of your pull requests and writes a descriptive comment about the changes in plain English. It analyzes the changes of your pull requests and gives you and your team a summary of all the changes in plain English. It uses the GitHub/GitLab API to get the diff of your pull request and then uses an AI model to generate a description of the changes.

In summary, "diff" can refer to a data comparison tool used in computing or an AI-powered app that reviews the diff of pull requests.