# module {#module}

A module in DolphinDB is a script file that only contains function definitions. When we need to call a specific function we can call the module that contains this function definition. A module is declared by a `module` statement which appears on the first line of a module file.

Modules are organized hierarchically. The naming structure must be consistent with the directory structure. Here is an example of a module declaration on the first line of a module file:

```
module example::ch9
```

In the example above, the module file is &lt;package root folder&gt;/example/ch9.dos. The root package folder is at &lt;DolphinDB Home&gt;/modules.

The module file name extension is ".dos", which stands for "dolphin script".

Related statement: [use](use.md)

**Parent topic:**[Programming Statements](../../Programming/ProgrammingStatements/programming_statements.md)

