Multi means “many” or “multiple.” Multidisciplinary design optimization (MDO) has become popular largely because it allows engineers to optimize over many different disciplines at the same time.
For example, you can use MDO to simultaneously optimize a vehicle body for structural, aerodynamic, thermal and acoustic behaviors. In addition, you can directly include non-performance measures, such as cost and manufacturability, in the optimization statement.
The key to accommodating so many disciplines is that MDO search methods are discipline independent. That is, they are not related to the physics of the problem in any way. Instead, MDO methods are either math-based or heuristic strategies that are used to search an unknown design space.
Sometimes there is the misconception that MDO methods should only be used for problems that involve many disciplines. But, in fact, MDO methods are often the best approach for design problems that consider only a single discipline.
This confusion can be avoided by taking a slightly different view. MDO methods can be applied to many different disciplines, whether one at a time, or several simultaneously. Because they are discipline independent, MDO methods can’t even distinguish between applications that involve a single discipline and those that are truly multidisciplinary. In this case, perhaps it’s true that ignorance is bliss.