Background: An extensive and international evidence base positions professional learning communities (PLCs) as an effective continued professional development (CPD) mechanism that can impact on teachers' practices and, in turn, students' learning. The landscape of teacher PLCs is continuously developing; notably through teachers' uses of social media. Yet, there is limited robust evidence identifying the characteristics of social media PLCs that impact on teachers' learning and practice. Purpose: This exploratory study examined the characteristics of a specific Twitter-based professional learning community -- #pechat. The research questions were: (i) what is the nature of a Twitter-based professional learning community? and (ii) what characteristics of a Twitter-based professional learning community develop learning and practice? Methods: Data were generated from 901 tweets between 100 participants; and 18 in-depth semi-structured elicitation interviews with participants and moderators of the Twitter-based professional learning community. Data were analysed through a process of deliberation, and a relativist approach informed quality. Findings: Two themes are reported to explain the nature of the Twitter-based professional learning community and the different types of characteristics of #pechat that developed learning and practice. The first theme "engagement" shows how different participants of #pechat engaged with discussions and how moderators played a key role in facilitating discussions between participants. The second theme "shared practices" shows how discussions between participants of #pechat led to the development of new practices that some teachers were able to use to accomplish particular objectives in their physical education lessons. Conclusion: The analysis of the data provided evidence to suggest that #pechat is a PLC and is representative of an established group of practitioners. These characteristics should be considered in the design of future online professional development experiences. Facilitator or moderator training could support the development of social media based PLCs that subsequently and positively impact on teachers' practices.