A label is one of the taxonomies defined by default in WordPress. They allow you to define the content of a post more precisely as keywords would do.

Unlike categories, tags are optional. There is no limit to the number of tags that can be added to an article, however good practice recommends that you do not use too many tags for the same post (this would be detrimental to your SEO).

Tags can be added, edited and removed via the menu Posts > Tags.