A d-module is a piece of computer code that can be used in a program or website. When you're writing code for a website or program, it can be hard to remember all the details you need. D-modules can be used to make it easier because they contain all the details a programmer needs to create a part of the program or website. For example, if a programmer wants to add a button on their website, they can use a d-module to add it easily and quickly.