k-factor : A model used to calculate how much virality your growth loop is getting. To be able to drive growth across time, you need a k-factor higher than 1.0
Building a growth loop is an iterative process that can take up to months or even years. Teams need to think about their product, sometimes re-think core features, tweaking them to be more actionable for the user. Finally, even if you drive growth, it won’t ensure the sustainability of your loop
Very useful piece on building growth loop.