In the culinary arts, the word Dijon (pronounced "dee-zhon") refers to a style of prepared mustard that originates in the Dijon region of France.
Here's a basic Dijon mustard recipe.
The traditional Dijon mustard recipe includes white wine and ground brown mustard seeds along with salt and other spices. Dijon mustard has a pale yellow color and slightly creamy consistency. Black mustard seeds can also be used in making Dijon mustard.
At one time, any product called Dijon mustard had to be made in the Dijon region of France. Other products could be called "Dijon-style mustard" or simply "dijon mustard" with a lowercase "D".
Today, however, the term Dijon mustard has become generic, so any mustard using the basic Dijon recipe can be called Dijon mustard.
Making dijon-style mustard is fairly simple — it's mostly a matter of grinding up mustard seeds and puréeing along with white wine, vinegar and salt. But it's important to soak the mustard seeds before using them, and you need to refrigerate the finished mustard for 24 hours before serving. See the recipe linked above for more details.