There has been some recent discussion about the philosophy of science and the movie Expelled in connection with ID and the intelligent design movement. Much of this has assumed that everyone is familiar with ID is. In order to make this more complicated, ID does not mean just one thing. It means a few things.
ID is sometimes taken to refer to a family of theories about the origin of information in the universe. These family of theories all state that some information or structure in the universe was created by an intelligent being. In this sense, ID is NOT a theory. This family includes any theories of alien design, all forms of Creationism and every theory that claims that God designed the constants or laws of the universe. It would do well to note that by this definition Darwin believed in an intelligent designer. I will call this the wide family definition of ID.
Sometimes ID is taken to refer to a different family of theories. These are the theories that claim that information created by an intelligent being is empirically detectable in principle. These theories do not necessarily claim that intelligent beings actually created anything at all! I will call this the empirical family definition of ID. It would be useful to note that both criteria are sometimes combined. In that case, the family of theories could be called the narrow family. This narrow family excludes all fideistic theories (ie. some versions of creationism) and still includes some versions of “alien creation” theories.
Sometimes ID does not refer to a family of theories, but to a particular theory of design. An example, now famous, is the design of the bacterial flagellum. Behe has claimed that this feature is designed. The structure did not originate from any mechanical process at all. The evidence is the claim that the formation of all such structures (irreducible complex ones) using any evolutionary process is highly improbable. This theory could (in principle) be disputed by other thinkers favorable to ID. It is one of many. There is no single Theory of Intelligent Design.
Sometimes ID refers to a research program or a heuristic. In that sense, one arrives at scientific theories by assuming that the object of study was designed. For example, one might suppose that so-called junk DNA has a useful function. One would then begin research to find out what that function might be. In this kind of case, ID is not a theory. It is a way of thinking that encourages scientific research.
Thus ends the list of what ID is. ID is not creationism. It lacks political agendas and faith commitments. ID is not the Intelligent Design Movement (IDM). ID is not a revision of creationism. It is both too general and continues much earlier thought. ID is three things: it is a theory about specific features of the world, a family of such theories, and a research program.