In January 2017 we clarified what was meant by not spamming in the directory.
Since then, the language has been tweaked slightly, but the crux of the matter remains as follows: Public facing pages on WordPress.org (readmes) must not spam
Public facing pages, including readmes and translation files, may not be used to spam. Spammy behavior includes (but is not limited to) unnecessary affiliate links, tags to competitors plugins, use of over 12 tags total, blackhat SEO, and keyword stuffing.
If you have a keyword or phrase repeated over 30 times in your plugin A plugin is a piece of software containing a group of functions that can be added to a WordPress website. They can extend functionality or add new features to your WordPress websites. WordPress plugins are written in the PHP programming language and integrate seamlessly with WordPress. These can be free in the WordPress.org Plugin Directory https://wordpress.org/plugins/ or can be cost-based plugin from a third-party, you’re probably spamming. There are exceptions, especially when a term is a common word or you’re listing your shortcodes. However please be reasonable. If we see you using the same word 50 or more times in the readme, you’ll likely be receiving a warning.
Please take these warnings seriously. If you get asked to fix one plugin, we expect you (and ask you) to take care of any plugins we didn’t list as well. Be mature humans.