It is common to use a variety of terms involving communication interchangeably. Public relations, publicity, communication, news, marketing and advertising get lumped together often. In fact, they are separate and distinct, and each has a role to play in promoting your organization.
For our purposes here, we will focus on publicity - selling news media on covering your organization/using your materials, and even serving your unit by "acting as your own news media."
Publicity should function as part of a larger communication process. It's best to look at publicity philosophically at first, because it helps to understand why we are doing something before we do it.