How is Oracle used in PL/SQL? Define the features of process and how they are defined?

PL/SQL - PL/SQL is Oracle's procedural language (PL) superset of the Structured
Query Language (SQL). PL/SQL is block-structured language that enables developers to code procedure, functions and unnamed blocks that combine SQL along with procedural statements. PL/SQL has its own processing engine that executes PL/SQL blocks and subprograms. If the host program does not have the PL/SQL engine, the blocks of code are sent to the Oracle server for processing. The subsequent figure displays the PL/SQL engine as integrated elements of Oracle server. The engine executes process statements and passes SQL statements to the SQL statement executor within the Oracle server.

Procedures - Sophisticated business rules and application logic can be stored as procedures inside Oracle. Stored procedures - groups of SQL and PL/SQL statements - permit you to move code that enforces business rules from the application to the database.

As a result the code will be stored once for all applications to use. Procedures can be described or created along with the CREATE PROCEDURE command. The syntax in Oracle to define a procedure is:
CREATE [OR REPLACE] PROCEDURE [.]
[( [IN|OUT|IN OUT]
[, [IN|OUT|IN OUT] ] ...)] {IS|AS}
[]
BEGIN

[EXCEPTION
WHEN THEN

[WHEN THEN

...
...]
[WHEN OTHERS THEN
]]
END;