A true object-oriented language like Java has a root class (in Java it is called Object, not surprisingly), from which all other classes are derived. PL/SQL is, officially, an object-relational language, but at its core it is a relational, procedural programming language and it has at its core a “root” package named STANDARD.
The packages you build are not derived from STANDARD, but almost every program you write will depend on and use this package. It is, in fact, one of the two default packages of PL/SQL, the other being DBMS_STANDARD.
To best understand the role that these packages play in your programming environment, it is worth traveling back in time to the late 1980s, before the days of Oracle7 and SQL*Forms 3, before Oracle PL/SQL even existed. Oracle had discovered that while SQL was a wonderful language, it couldn’t do everything. Their customers found themselves writing C programs that executed the SQL statements, but those C programs had to be modified to run on each different operating system.
Oracle decided that it would create a programming language that could execute SQL statements natively and be portable across all operating systems on which the Oracle database was installed. The company also decided that rather than come up with a brand-new language on their own, they would evaluate existing languages and see if any of them could serve as the model for what became PL/SQL.
In the end, Oracle chose Ada as that model. Ada was originally ...