The physical environment can be defined as that which operates on an ongoing basis regardless of the persons in it. This physical environment then affects the actions of and outcomes concerning the people within it.
The physical environment includes land, air, water, plants and animals, buildings and other infrastructure, and all of the natural resources that provide our basic needs and opportunities for social and economic development. (Ministry of Social Development, New Zealand)
Say, for example, you are playing sport and it is a windy day. You have to adjust your game to ensure that you allow for the way the wind is blowing.
All processes and behaviors take place within specific physical environments. Within a classroom for example
lighting, acoustics, size, comfort, safety, access to technology, etc.
create and add to a physical environment that is either conducive to learning or perhaps distracting.
Therefore a simple definition of any physical environment would be your natural surroundings - including whether it is clean or dirty and the things within it and how they interact to create a 'space.'