If you're frequently using the same term in your document, it would be annoying to type it again and again. What if you later decided to change that term or its formatting? To avoid searching and replacing in the whole document, LaTeX allows you to define your own commands in your preamble. They are also called macros . Give it a name. Later in the document you just need to use this name whenever you want to change this term. We need to do it just once in the macro definition. This will affect the whole document. Let's see how it works.