So what is platform?
My personal definition is that platform is a buildup of readership and/or a following of people who like to read what you write enough to buy and/or promote it. The bigger your platform, the higher your ability to sell your books in large volume and to get your books published through a publisher.
I'd like to point you to some great articles that have been written on this topic:
What are your thoughts on platform? Are you feeling overwhelmed by this buzz word? Have you been able to implement what you learn? What are your most difficult challenges in building a platform?