In Java, an identifier is a name given to a class, method, variable, package, or interface that allows the programmer to refer to the specific item from any place in the program. Identifiers are a fundamental concept in Java programming and must be named according to specific rules. The general rules for naming variables are:

• Names can contain letters, digits, underscores, and dollar signs.
• Names must begin with a letter.
• Names should start with a lowercase letter and cannot contain whitespace.
• Names can also begin with $ and _ (but it is not recommended to use them).
• Names are case-sensitive.
• Reserved words (like Java keywords, such as int or boolean) cannot be used as names.

It is recommended to use descriptive names in order to create understandable and maintainable code. Choosing meaningful identifiers improves code readability and maintainability. It makes the code easier to understand for developers and helps in avoiding naming conflicts.