On a shortcode example like this: [wp_show_posts name="Sidebar Latest Posts" settings="taxonomy=category&tax_term=humanities"]
the taxonomy=category part specifies the taxonomy. This is changeable depending on what taxonomy terms you want displayed for specificity. The most common values for this are category which is for post categories and post_tag which is for tags.
the tax_term= specifies the taxonomy term you want to display. The value to be added should be the slug of the taxonomy term.
So for example, if you want to display posts from Tags taxonomy of term “Historical Drama” w/ a tag term slug of historical_drama, you do it like this with the shortcode: