Evolutionary iterative development implies that the requirements, plan, estimates, and solution evolve or are refined over the course of the iterations, rather than fully defined and "frozen" in a major up-front specification effort before the development iterations begin. Evolutionary methods are consistent with the pattern of unpredictable discovery and change in new product development.
Adaptive development is a related term. It implies that elements adapt in response to feedback from prior work feedback from users, tests, developers, and so on. The intent is the same as evolutionary development, but the name suggests more strongly the feedback-response mechanism in evolution.
Some methods or methodologists emphasize the term "iterative" while others use "evolutionary" or "adaptive." The ideas and intent are similar, although strictly speaking, evolutionary and adaptive development does not require the use of timeboxed iterations.