(For the full post explaining the reasoning behind these code snippets see here.)
Add a “details” field to the Add New Product Category page
To get started, let’s add a text area to the product categories page. We’ll call it “details”. This lets us enter some detail about the product category as we create it. Because this form is quite narrow we won’t make it a full-on WYSIWYG visual editor. We’ll save that for in a moment.
Add a WYSIWYG “details” field to the Edit Product Category page
Next we’ll add the details field to the edit product category page. This time, because we’ve got more space, we’ll use a proper WordPress visual editor. That way you can use headings, blockquotes and include images and other media as if you were editing a page or post.
Save the details field content to the database
We need to save the details field when a product category is first added and after it has been edited.