How can a brief name an audience and avoid stereotyping people?
Tell your team who the piece is for by describing what that reader is trying to do, what they already know and the question on their mind. Then say what the piece won't try to cover. A brief that appeals to everyone gives a writer nothing to choose between.
A demographic label alone can mislead, since people with similar backgrounds may need very different information at different moments. Describe the reader's task, starting knowledge and immediate question instead.
Saying what the piece skips is part of the brief
An introductory article may not answer a specialist implementation question. A comparison may not suit someone who hasn't identified their requirements yet. Write those limits down, then review the draft against them. Cut explanations that distract from the task, and add context the reader needs to follow the argument.
The boundary comes from relevance to the task. You can still welcome readers beyond the core audience without making the brief responsible for every possible need. A clear audience gives the creative team a reason to pick one explanation over another.
What to try this week
Take your last brief and add one line saying what the piece won't attempt. Then read the draft against it and see what you'd cut.