The American Association for the Advancement of Science (AAAS) cites evolution as a core concept of biology, yet studies have found that biology students often exhibit low acceptance of evolution. As such, much of evolution education research aims to identify the causes of evolution rejection and develop instructional strategies to increase acceptance. This research relies upon surveys that measure evolution acceptance. Survey validity is an essential component of research quality, and a thorough definition of the construct of interest is critical for survey development and validity assessment. Thus, the purpose of this study was to develop a detailed, consensus-based definition of what constitutes "full acceptance of evolution" within the context of undergraduate biology education. This study used the Delphi method, in which a panel of experts was iteratively surveyed to establish a definition of evolution acceptance. As expert panelists voted on a definition, we found that (a) all agreed that evolution acceptance can be compatible with religious belief, and (b) "full acceptance" requires knowledge of certain aspects of evolution, including the shared ancestry of all life and existence of extensive supporting evidence for evolution. This definition serves as a foundation for establishing a survey that more accurately assesses students' awareness and assent with key aspects of evolution. [This is a paper in: "Proceedings of the 16th Annual Research of the National Association of Biology Teachers."]