A writer's platform is supposed to be important in attracting the attention of agents and/or editors. To me "platform" is a somewhat squishy concept. As I understand it, "platform" seems to encompass both the writer's credentials for writing this specific story ("How do you know about the subject matter you write about") and the writer's agenda ("What is your purpose? Who is your audience?").
At first I was annoyed by the necessity to address this complex issue in a three or four paragraph query letter. My personal inclination would be to focus only on the story in the query, and get into platform and all that other stuff at the next step in the process. But I suppose there are lots of well-written books that have no market or which may be full of errors because the author doesn't know what she's writing about.
What is my platform? I'm a middle aged woman writing stories for and about other mature women. My purpose is primarily to entertain the reader by telling an interesting story. To the extent the stories have a message it is that women are stronger than they think they are and that sometimes good things can come from a lot of unexpected sources if we are open to them.
I'm sadly afraid that's not unique enough. It needs more work. More specifics. Back to the drawing board.
How do you describe your platform in queries?