// GTM
Viral Coefficient
Also known as K-Factor
The number of new users each existing user brings in, on average. Sustained growth requires k > 1.
In depth
K-factor = invitations sent × conversion rate. Slack, Dropbox and Calendly had structural virality; most SaaS does not. Confusing 'word of mouth' with virality is a common founder trap.
Related terms
Activation Rate
% of new signups who complete the defined activation event within a defined window.
PLG
Product-Led Growth, a GTM motion where the product itself is the primary acquisition and expansion driver.
Referral Loop
A programmatic incentive that turns satisfied customers into a repeatable acquisition channel.