PMF (Product-Market Fit)
The point at which users pull the product from you instead of you pushing it to them.
PMF is the moment your growth stops being effort-driven and starts being demand-driven. Symptoms: retention curves flattening, organic word-of-mouth, users describing the product to peers without prompting, support requests shifting from "how do I do X?" to "when will you build Y?" The classic Sean Ellis test: if 40%+ of users say they'd be "very disappointed" without your product, you have PMF. Most indie founders think they have PMF before they do — real PMF is unmistakable in retrospect but ambiguous while you're in it.
Related terms
Retention
The percentage of customers who stick around. The inverse of churn, but usually tracked by cohort.
Wedge
The narrow initial use-case that opens the door to a broader product later.
MRR (Monthly Recurring Revenue)
The predictable monthly revenue from active subscriptions. The indie-founder scoreboard metric.