Reply To: check if posts are in custom taxonomy

But the problem is, that posts can’t have taxonomies – posts can only have terms from custom taxonomies associated to them.
Taxonomies are the “group” for terms, for example categories are part of a taxonomy called “categories” etc..

If you want to check if the post is in a specific category, then use the has_term() function. With this you can check if a post is within a specific category or any other taxonomy term.