Tags & Categories
Tags and categories are both WordPress taxonomies that can be applied to posts (but not pages), to help you organize your site’s content by topic. If you compare your WordPress site to a book, categories are like the table of contents, and tags are like the index.
Categories typically describe the site’s main organizational divisions, and tags provide a way to follow concepts or keywords that span across multiple topics. You can use either categories or tags on your site, or both in conjunction.
Sample site taxonomy: My Recipes
If your site were a collection of cooking recipes, your categories might include meats, vegetables, breads and soups. You could create another set of categories that described your content along another axis- appetizers, main courses, desserts. A single post can belong to multiple categories - so you post "French Onion Soup" could belong to both the soup category and the appetizer category.
The tags for this site might include specific ingredients (e.g. kale or milk) or dietary restrictions (e.g. vegan or gluten-free). While these concepts are important, they might not make sense as the primary organization principles for your site.