Environmental psychology can mean one of two related things:
1) An interdisciplinary field focused on the interplay between humans and their surroundings.
Various researchers have also termed this environmental social sciences, architectural psychology, socio-architecture, ecological psychology, ecopsychology, behavioral geography, environment-behavior studies, person-environment studies, environmental sociology, social ecology, and environmental design research.
This is an unusual use of the term - choosing another term would be desirable for clarity.
This subject is discussed at the Appropedia page on Psychology.