Engineering education has become increasingly multidisciplinary in order to prepare future experts to transcend disciplinary boundaries and to co-construct solutions to solve grand challenges. However, faculty members' perspectives and experiences have been largely ignored in the literature. To understand and support faculty members, the present study investigated faculty members' conceptualisations of multi-, inter-, and transdisciplinary education. We conducted semi-structured interviews with 13 faculty members from engineering, business, art and design with varied experiences with multidisciplinary teaching, course design, and programme management. We found that while some faculty members conceptualised multidisciplinary education as an encompassing concept, most used disciplinary integration to distinguish multi-, inter-, and transdisciplinary education. However, their conceptualisations of the differences between multi-, inter-, and transdisciplinary education were nuanced. Summarising the perceived nuances in different aspects of course design, we propose a typology to demonstrate the variety of types in faculty members' course design. By identifying the diversity and complexities of faculty members' conceptualisations, this study attempts to help faculty members achieve an in-depth understanding of their conceptualisations and practices, as well as support engineering educators in designing courses with disciplinary integration.