The scientific literature points to the importance of reflection and its contribution to teachers’ work. However, the reflective process involves some challenges. Definitions of reflection are abstract, and models of reflection are complicated and not always accessible to practitioners. The goal of this study was to unpack the concept of reflection into categories – actions or phases which are part of a comprehensive reflective process. For this aim, we analyzed 11 mathematics teachers’ reflective expressions, collected in three different settings of professional development. Six categories of reflection were identified in the study, which suggest different actions that teacher educators can consider when designing guiding tools to support teachers through the reflective process.