a clause or phrase that utilizes a stative verb, such as IS or HAS and generally has no object, just a subject and verb. The door opened. The tree was big. There is nothing wrong with this construction, however, when it occurs frequently, it makes for sluggish and flat writing. Therefore, the first example, The door opened can be converted to Donald opened the door. The second, The tree was big, can become a fragment - Big tree. We are encouraged to refrain from passive sentences, because in general writing, it makes for a weak delivery of information. However, using the passive voice is an important technique in writing, the use of which can allow the reader to fall into the scene on a pastel cloud. (The last 2 sentences were passive voiced). Passive voice is discouraged for action sequences (duh) and narrative. Editors who attack every passive voice sentence should be questioned, because they are being slaves to a rule. However, an author needs to recognize every passive voice clause and question its existence, usually in revision, because when drafting, passive generally predominates, because the human brain favors its use, but readers are rarely engaged by it. There is a whole science that authors must know about the difference between writing and Reading, the one being the brain engaged to the hand and the other being the eye engaged to the brain. But that's another story.
Edward C. Patterson