Even though research exists on interdisciplinary education and interdisciplinary skills, the term "interdisciplinary" is ambiguous. Currently, studies on how different internal stakeholders in an education setting define and conceptualise interdisciplinarity are lacking. Consequently, the purpose of this paper is to define and conceptualise interdisciplinarity in higher education. This is investigated by focus group interviews with 29 internal stakeholders representing students, teachers, and program managers at an interdisciplinary master's program. The conclusion provides a definition of interdisciplinarity; The integration of people possessing different competencies (knowledge, background, and skills) acting upon an identified need, challenge or opportunity that requires a holistic approach founded in synergies and thereby creating new knowledge. Interdisciplinary learning is mainly conceptualised to take place in open-ended and research-like innovation projects.