Programmatically create a term?
You know that you want something from taxonomy module so first you need to look in Drupal\taxonomy\Entity -- or the corresponding directory -- you will find the Term class there. Now look at the annotation, it says @ContentEntityType and in there:

*   entity_keys = {
*     "id" = "tid",
*     "bundle" = "vid",
*     "label" = "name",
*     "uuid" = "uuid"
*   },


So, what you want is

$term = Term::create([
  'name' =&gt; 'test', 
  'vid' =&gt; 'client',
])-&gt;save();


because the label entity key is name and the bundle entity key is vid. I added a -&gt;save() call as well as I presume you wanted to save it too.