Mayer and Lloyd (2011, p.3) offer
in Knapp’s (2003) review, professional development includes ‘the full range of activities, formal and informal, that engage teachers or administrators in new learning about their professional practice’ (p.112), while professional learning refers to ‘changes in the thinking, knowledge, skills, and approaches to instruction that form practicing teachers’ or administrators’ repertoire’ (pp. 112- 113). Thus professional learning could involve changes in one’s capacity for practice (i.e., changes in professionally relevant thinking, knowledge, skills, and habits of mind) and/or changes in practice itself (enacting the new knowledge and skills in one’s daily work).
But go onto use an "encompassing definition" of both development and learning offered by Day and Sachs (2004)
… all natural learning experiences and those conscious and planned activities which are intended to be of direct or indirect benefit to the individual, group or school and which contribute … to the quality of education in the classroom. It is the process by which, alone and with others, teachers review, renew and extend their commitment as change agents to the moral purposes of teaching and by which they acquire and develop critically the knowledge, skills and emotional intelligence essential to good professional thinking, planning and practice with children, young people and colleagues through each phase of their teaching lives. (p. 34)
Mayer, D. Lloyd, M. (2011) Professional Learning: An introduction to the research literature