What is an example of freemium?

Could you please elaborate on what an example of freemium might be? Is it a type of business model where basic services are offered for free, but users have the option to upgrade to premium features for a fee? If so, could you provide a specific instance of a successful freemium model that's been implemented in the world of cryptocurrency or finance? I'm particularly interested in understanding how this model works in practice and how it benefits both users and the company offering the service.