No singular definition of teacher leadership (TL) exists in empirical literature or practice in the field. This lack of clarity has greatly impacted the implementation of TL in American schools. The purpose of this study qualitative case study was to investigate public school principals' perceptions and understandings of TL in an effort to better inform continued efforts toward its ubiquitous application in American schools. Principals' definitions of TL fell into three categories: action-based, quality-based, and role-based definitions. Principals' recognition of the work of teacher leaders in schools fell into two parallel categories: action-based and role-based leadership. Findings reveal that many principals appear to have not yet "caught" any waves of TL beyond the second. More in-depth research is required to determine the accuracy of this evaluation and how to best encourage principals to extend their understanding of and openness to TL.