In Python, a module is a file containing Python definitions and statements. The file name is the module name with the suffix .py. Modules can be imported and used in other Python programs to provide additional functionality.

Here are some commonly used modules in Python:

1. math: Provides mathematical functions and constants.
2. random: Generates random numbers and performs random selections.
3. datetime: Manipulates dates and times.
4. os: Provides a way to interact with the operating system, such as accessing files and directories.
5. sys: Provides access to some variables used or maintained by the interpreter and functions that interact with the interpreter.
6. re: Provides regular expression matching operations.
7. json: Provides functions for working with JSON data.
8. csv: Provides functions for working with CSV files.
9. urllib: Provides functions for working with URLs.
10. requests: Provides functions for making HTTP requests.

These are just a few examples, and there are many more modules available in Python’s standard library as well as third-party modules that can be installed using package managers like pip.