An ad hoc committee is a committee that is appointed by Parliament for a specific purpose or task. It is not a permanent committee and is formed as and when the need arises. The term "ad hoc" means "for this purpose" in Latin.
Option 1: A joint committee is a committee that is created by Parliament with members from both the House of Commons and the House of Lords. It is not specifically appointed for a particular purpose.
Option 2: A permanent committee is a committee that is established by Parliament on a continuous basis to handle specific areas of responsibility. It is not appointed for a specific purpose.
Option 3: A standing committee is a type of permanent committee that exists in some parliaments. It is responsible for reviewing and considering legislation and other matters, but it is not created for a specific purpose.
Based on the given options, the correct answer is 4: Ad hoc Committee.