noun. 1. basically, joint consent, unity, or acclimation with others. 2. with regard to the phenomenological personality theory of Carl Rogers, (i) the requirement for a professional to behave in alignment with their authentic feelings instead of with a preset or ideal perception of what a therapist should be or act like, or (ii) the aware incorporation of an encounter into the individual. 3. with regard to environmental psychology, reference: person-environment interaction.