An environmental portrait is a portrait taken in a location that helps to express the personality of the subject. This can be a place where the subject works or plays, or a room in their own home. The act of moving outside a studio must have a reason, something that it adds to the expression of personality.
The choices of lens, white balance, and any other technical considerations are limitless, but should all be consciously made for the purpose of taking the best shot possible. Like many other forms of photography, portraiture seeks to be more than the literal representation that a simple recording of facts is limited to.
You would be surprised how much easier it is to ask someone if you can take their picture while they work than it is to ask them to be photographed outside of their environment of choice.
None thus far.