From ResearchID.org, a nexus for researching Intelligent Design:

Intelligent design is the scientific investigation of intelligent causation and subsequent novel data, hypotheses, experiments, and practical applications that are derived by viewing specific phenomena in the universe as designed. Intelligent design is a scientific hypothesis that seeks to explain a very large range of scientific data, and so has a general definition, and then subsidiary definitions for use within specific disciplines.

Overview of Intelligent Design

Intelligent design (also known as "ID") is an empirical approach to the scientific study of how nature works. Theorists and researchers exploring the idea of intelligent design are seeking to derive an understanding of nature from scientific data and the cause-and-effect structure of the universe.

First, ID scholars consider what the scientific data tells us about the types of physical effects that are known to be produced only by intelligent causes. A few examples of effects of intelligence are novel and independent functional information, novel functional machines, and highly constrained goal-oriented processes. In this way, design theorists are investigating which effects can only be caused by intelligence. In order to determine this, a scholar must have a great deal of scientific knowledge about what unguided processes can do, and an objective evaluation of what unguided processes cannot do.

Second, ID scholars ask whether these types of structures can be found in nature. By consulting the cause-and-effect structure of the universe, and considering which causes result in which effects, it can be clearly seen that, in fact, many phenomena found in nature are only known to be caused by intelligence. Some claim that physics and chemistry can explain the information in DNA, but natural laws do not dictate the sequence of bases in a gene. As Polanyi noted, "the information in DNA could no more be reduced to the chemical than could the ideas in a book be reduced to the ink and paper: something beyond physics and chemistry encoded DNA." When these facts are considered, it is then seen that there is a great deal of scientific evidence that there are effects in the physical world that can only be caused by intelligence. Scholars open to intelligent design propose that specific physical phenomena in nature are better explained, and scientifically studied, as being designed by intelligence. The constant use of design language in biology demonstrates that it is better studied and understood as designed by intelligence.

Simply stated, ID begins by asking, "Can we scientifically detect if something was designed by intelligence?" Detecting design is a scientific possibility, and ID scholars think this ability is essential for a proper contextual study of the universe. Intelligent design seeks to find natural objects that contain the same final conditions, or physical histories, as objects that science knows were intelligently designed, based upon our observation of intelligent agency in the natural world. An important goal of research from a design perspective is to understand intelligence working in the context of the physical world, and infer intelligent activity by observation and analysis of data.

Equally or more important as the above explanation, is what follows from it: ID also proposes that specific physical phenomena in nature are better studied as being designed by intelligence. Because of this, intelligent design has been applied in the form of working scientific research programs by which novel data, hypotheses, experiments, and practical applications are derived by hypothetically viewing phenomena in the universe as designed, whether the researcher holds that the objects of study are actually designed or not.

So intelligent design is an inference, from the strength of empirical knowledge alone, that specific phenomena are caused by intelligence, and that these phenomena are better studied as instances of design.