Intelligent Design is the premise or theory that Man and the animal world did not come to be from a process of evolution, i.e. - Darwin's Theory of Evolution but rather through the work of a Designer/Creator Being.
Intelligent Design Theory holds that we see very complex systems in the makeup of man and the animal world with interdependent components, whereby the complex whole, could not have come into being one part at a time. For any single part cannot serve as a functioning mechanism or the whole system will not function.
Thereby, the system must be complete with all it's components right at the beginning, or it could not function at all. Some call this "Irreducible complexity."
This is not magic as some have labled it, but it is plain simple logic, easily proven by example.
This means there had to be a designer in the process at the beginning for it's very existence.
Some may call this designer a Super Intelligent Being, without specifying who or from where, and some identify this Being as God.
** See the link on "Credit Where Credit Due" for further clarification.