The idea of product market fit is actually pretty obvious. What it means is that your product (or service) fits a need in the market (or target market), and you found it because you are getting traction (or sales).
For you tech minded folks (like me), here is a formula for you:
fit = traction(product)
So, what is traction then? The easiest way to measure traction is by sales. If you can get sales, you have traction. How much? It depends on the amount of effort and cost associated with getting the sale. The easier the sale (and happier the customer) the more traction you have. Sales is not the only way to measure traction. You could measure it by ‘free trial subscribers’, by ‘letters of intent’, or even by ‘customer surveys’. However, sales with positive customer feedback is the highest level of traction.
So, go out and get some. Traction that is.
And this book is a great place to learn how to do that: