Best practice and style are at the core of every program; there is always a better way to do something. Policy helps programmers determine how something should be written.
Policy is a more or less ambiguous way of describing the best way to do something in programming. This can often be described as "best practice" when writing a program. This can pertain to the way a method returns a value, the way inheritance is structured, and the way to exit a loop, among other things, and it can vary from language to language.
Many companies often have their own sets of internal documentation referred to as Coding Standards that enforce policies which they determine to be valuable for maintenance and readability purposes of their code base.
You can learn more about policy and programming paradigm here.
