Defining a writer should be easy. A writer is someone who writes. However, most of us learn to string words into sentences in grade school, so we all can claim to be writers.
We could define a professional writer as someone paid to write. That narrows the field considerably. But within the entertainment industry, where I have spent the entirety of my professional life, there are many who write as a means to an end. They write to get their first directing gig, to secure their next producing job, or to make a boat-load of money. If you’ve sold a script or have been hired to write, you can be deemed professional. Writing stories as a means to an end does a disservice to all. You wouldn’t want to listen to a musician who only picked up the guitar in hopes of getting that lucrative sheet music publishing deal. Better to hear someone play because they love to make music. Thinking thus, I feel the need for a more refined definition of what makes a writer. Here is mine.
A writer is someone who can’t stop themselves from writing.
Just to be clear, I apply this standard to the other arts as well. A painter can’t stop painting. A dancer has to dance. A sculptor…well, you get the idea.