Several academic departments have increased their use of active learning to address low student success rates. However, it is unclear whether those implementing active learning have a consistent conceptualization of it. Like other educational terms, the phrase "active learning" is in danger of becoming overused and misunderstood, which puts the utility of active learning into question. This study examines 115 conceptualizations of active learning across six institutions of higher education that are infusing more active learning into their mathematics courses. We use the four pillars of inquiry-based mathematics education as a basis for analyzing these conceptualizations and compare them in two ways: by stakeholder role and by institution. Our findings show that many participants conceptualize active learning as student engagement and activities other than lecture, yet there was limited focus on the role of the teacher and content. Only eight participants mentioned issues of equity. Comparison within individual institutions shows that faculty within departments may hold common understandings of active learning. Implications of these findings include a need to develop an understanding of active learning that attends to all four pillars and is shared across departments, institutions, and disciplines.