What are the different categories of PL/SQL program units?

A named block is a PL/SQL block that Oracle stores in the database and can be called by name from any application. A named block is also known as a stored procedure. Named blocks can be called from any PL/SQL block. It has a declaration section, which is known as a header. The header may include the name of a block, type of the block, and parameter. The name and list of formal parameters are known as the signature of a subroutine. Once a named PL/SQL block is compiled, it gets permanently stored as p-code after compilation in the shared pool of the system global area. Therefore, the named block gets compiled only once. An anonymous block is a PL/SQL block that appears in a user's application and is neither named nor stored in the database. This block does not allow any mode of parameter. Anonymous block programs are effective in some situations. They are basically used when building scripts to seed data or perform one-time processing activities. They are also used when a user wants to nest activity in another PL/SQL block's execution section. Anonymous blocks are compiled each time they are executed.