There are some basic rules to be maintained while writting any program. These rules specify the way by which a developer should develop their applications. No common stardard exists for coding an application, but the people having extensive coding experience suggested a way to write a code in a fashion that makes it easy for them as well as for others to understand code and maintain it.
Coding rules and coding standards are two different things.
Coding standards are somewhat related to how to write a code. It may or may not be specific to programming language. There are some generic standards which doesn't depend on langauge choosen for coding. For example, the way to comment a code.
In short coding rules are consider as a design level entity while coding standards are consider as a coding level entity.