A complex question, trick question, multiple question or plurium interrogationum (Latin, "of many questions") is a question that has a presupposition that is complex. The presupposition is a proposition that is presumed to be acceptable to the respondent when the question is asked. The respondent becomes committed to this proposition when he gives any direct answer. The presupposition is called "complex" because it is a conjunctive proposition, a disjunctive proposition, or a conditional proposition. It could also be another type of proposition that contains some logical connective in a way that makes it have several parts that are component propositions.
Complex questions can but do not have to be fallacious, as in being an informal fallacy.
One form of misleading discourse involves presupposing and implying something without stating it explicitly, by phrasing it as a question. For example, the question "Does Mr. Jones have a brother in the army?" does not claim that he does, but implies that there must be at least some indication that he does, or the question would not need to be asked. The person asking the question is thus protected from accusations of making false claims, but still manages to make the implication in the form of a hidden compound question. The fallacy isn't in the question itself, but rather in the listener's assumption that the question would not have been asked without some evidence to support the supposition. This example seems harmless, but consider this one: "Does Mr. Jones have a brother in jail?"
In order to have the desired effect, the question must imply something uncommon enough not to be asked without some evidence to the fact. For example, the question "Does Mr. Jones have a brother?" would not cause the listener to think there must be some evidence that he does, since this form of general question is frequently asked with no foreknowledge of the answer.
The complex question fallacy, or many questions fallacy, is context dependent; a presupposition by itself doesn't have to be a fallacy. It is committed when someone asks a question that presupposes something that has not been proven or accepted by all the people involved. For example, "Is Mary wearing a blue or a red dress?" is fallacious because it artificially restricts the possible responses to a blue or red dress. If the person being questioned wouldn't necessarily consent to those constraints, the question is fallacious.