[K-factor](https://en.wikipedia.org/wiki/K-factor_(marketing)) is a metric used in marketing to measure the virality of a product or service. It originates from epidemiology, where it describes the reproduction rate of infections, and has been adapted to quantify how effectively users recruit new users. The K-factor is calculated by multiplying the number of invitations each user sends by the conversion rate of those invitations. A K-factor greater than 1 indicates that each user is bringing in more than one additional user on average, leading to exponential growth. Conversely, a K-factor less than 1 suggests that growth will eventually plateau without external input.
