There is increasing interest in the provision of online professional development (OPD) for teachers. This case study contributes to the field of research on professional development in the context of activities and discourses relating to mathematics teachers' synchronous oral communication online. The purpose of this article is to explore the activities on offer in this communication and to identify the discourses that mathematics teachers may create in their meaning-making activities. An analysis of an online community in the form of a professional development course for mathematics teachers has, therefore, been conducted. The analysis shows that there is a lack of reciprocal participation and a shortcoming in creating a reflective learning environment, which can probably be partly explained by the specific mode of digital conversation. The discourses created by the mathematics teachers in their meaning-making activities focused mainly on sharing experiences about the teaching of mathematics.