Thanks Long. That worked.
Note for others : the value "3" on the screen capture you linked to, must correspond to the ID of the taxonomy's value ("Yes" in my case).
For the record : I finally decided to create two "Radio list" values for the taxonomy ("Visible") : "Yes" and "No". The portfolio grid on the welcome page queries all posts that have the "Yes" taxonomy value. This way the client can decide if the post will show on the Home page of his website.