What is the difference between a regular and a weak and a regular entity?

A regular entity, also known as a strong entity, has a primary key that uniquely identifies each instance and can exist independently of other entities. In contrast, a weak entity does not have a sufficient primary key and relies on a "strong" or "regular" entity for its identification; it is dependent on the strong entity for its existence and typically has a partial key. Weak entities are often used to represent a relationship that requires more context, while regular entities stand alone as distinct objects in a database.