Dashicons are what’s known as an icon font and were added to the core of WordPress with the release of 3.8. The icons are vector based so they can be as large or small as you want without losing quality. Plugin authors can use CSS, HTML, or a Glyph for use within Photoshop to display an icon. While 3.8 had 167 icons, WordPress 3.9 shipped with 30 new Dashicons bringing the total to 197.

The icons cover Media, TinyMCE, WordPress.org, Sorting, Widgets, Alerts, and Miscellaneous. Some plugin authors have already opted out of using a bitmap image and are using a Dashicon to represent their plugin within the WordPress admin menu. If none of the Dashicons match your use case, try Genericons instead. Genereicons is also an icon font but has icons that are not focused on WordPress.
Permalink
Are there any “average WP user understandable” instructions on how to use them? Did try to find out but didn’t understand a single line of code and how to implement those icons in posts. Maybe it’s only me but not so sure.
Report
Permalink
Dash icons are meant to be used by developers, see this http://wpsites.net/web-design/adding-dashicons-in-wordpress/
Report
Permalink
All I get at this page is: Forbidden.
Report
Permalink
There are also undocumented bbpress dashicons which I managed to successfully add to the site I am developing.
.dashicon-forum:before {
content: "\f449";
}
.dashicon-topic:before {
content: "\f450";
}
.dashicon-reply:before {
content: "\f451";
}
Report
Permalink
I saw those were added in the ticket but didn’t see them in the official announcement post. Thanks for adding those in the comments.
Report
Permalink
It took some effort to get them to work. In the end I copied the font data to a directory in my child theme and the relevant css to the child theme’s CSS.
Report
Permalink
Maybe helpful, a plugin that list all icons and help with a picker for Dahsicons
https://github.com/bueltge/WordPress-Admin-Style
Report