Each project's maintainers provide PyPI with a list of "Trove classifiers" to categorize each release, describing who it's for, what systems it can run on, and how mature it is.
These standardized classifiers can then be used by community members to find projects based on their desired criteria.
Note: As of PEP 639, the use of License Trove classifiers is deprecated. Please use license expressions in your pyproject.toml instead.