What's in a name? That which we call a rose by any other name would smell as sweet.
--William Shakespeare
A naming convention is a convention for naming things. In database or Programming, it is a convention for naming attributes or objects. Naming standards are some rules or guidelines which help to work as a team faster. It most probably won't affect database performance although they will surely affect performance and level of understanding of designers, developers and support staff. With a consistent naming scheme they will understand data models better and produce SQL statements faster. And this will directly affect your project costs.
There are some naming standards described below for Oracle Database Design. They could probably be used not only in Oracle but in other RDBMS's as well (for example MySQL, PostgreSQL, SQLite) but you should check whether they haven't other widespread standards.
It is very important to follow some naming standards and guidelines in the process of designing Oracle databases. It is even more important if you have a task to design an Oracle database containing hundreds of tables and thousands of other objects. If you have a project command of several people it is absolutely necessary to pick a naming convention, write it down and USE it.
Human understanding:
Maintain standards so that everybody is in the same alignment and understanding easily.
Framework and Application understanding:
Maximum framework or development technology has CRUD operation which speeds up development. A well-defined naming scheme becomes more important when you adopt object relational mapping (ORM) technologies or automatic code generation. Naming convention is very important in this operation because all labels on the page automatically convert into human language if naming is standard.