Cogent argument for better understanding of the take-up of teacher professional development through understanding the definition itself has been presented. The main constituents of the definition with reference to different sources of information in psychology, philosophy and pedagogics have been analyzed. To make the research more logical, the definitions "personality development," "professional development" and "teacher professional development" have been studied in consecutive order. The literature review, which is based on Ukrainian and foreign documents observation, shows different approaches to defining the notion studied: a process-based approach and a system-based approach, as well as their conditional character and appropriateness. In the authors' view, teacher education is a key issue in basic development sectors of any country of the world. Teachers' professional activities must not focus on individual content only but bear in mind students' intellectual, spiritual, physical, moral, social and cultural well being. Teacher professional development is a powerful and effective premise for sustained improvement of student outcomes. On the whole, teacher professional development can be defined as a long-term complex process of qualitative changes in teaching aimed at teacher performance improvement in the classroom and ensuring students' success. According to the study, this process can be compulsory or so called optional. The effectiveness of professional development is structured: leadership, knowledge, available resources, high level of collaboration, appropriate evaluation and sustainability.