What is a freemium app?

Excuse me, could you possibly elaborate on the concept of a freemium app? As I understand it, this term refers to an application that is available for free download but also offers additional features or services for a fee, correct? Is there a particular model that freemium apps typically follow in terms of their pricing structure and the types of features that are made available for free versus those that require payment? And are there any benefits or drawbacks to using a freemium app compared to a traditional paid or free application?