Freemium Model

Freemium is a pricing strategy by which a product or service is provided free of charge, but money (premium) is charged for additional features, services, or virtual (online) or physical goods.

In SaaS, this is a powerful User Acquisition strategy (e.g., Slack, Dropbox). It lowers the barrier to entry, allowing rapid adoption ("land"), with the goal of upgrading heavy users or teams to paid plans ("expand").