A principle can be defined as a "fundamental truth or proposition that serves as the foundation for a system of belief or behavior or for a chain of reasoning."
EA guiding principles, then, are high level rules that are followed to guide the architectural implications of Forest Service investment and design decisions.
Facilitate behavior change
Describe preferred practices
Reflect vision of improved ways of using technology to benefit business
Reflect high-level business &IT requirements in a commonly understood way
Provide guidance that applies across the business: to help architects, designers, developers
Capture the "spirit" of the architecture
In order to be meaningful, principles need to be shared and authorized. This takes time. The Forest Service Enterprise Architecture is in the process of setting up teams and working groups to handle these tasks. More change is on the way. We are just in the first phase of this process.
The corresponding USDA EA principles are available here.