Site icons recently landed in trunk using the terminology “Site icon”. We didn’t go with “favicon”. Favicon is an under-the-hood term, one with a lot of tedious history. Instead, we want to package title, tagline, and icon together as site identity. And, we already have some history with site/blog icon. Here’s a quick visual survey A visual survey is a collection of screenshots for a like set of screens or interfaces, such as all list table screens or all toolbar incarnations across various devices. These screens are not presented in the context of a particular flow.https://make.wordpress.org/test/tag/visual-survey/.
4.3 Beta A pre-release of software that is given out to a large group of users to trial under real conditions. Beta versions have gone through alpha testing in-house and are generally fairly close in look, feel and function to the final product; however, design changes often occur as part of the process. uses “Site Icon”
wordpress.com An online implementation of WordPress code that lets you immediately access a new WordPress environment to publish your content. WordPress.com is a private company owned by Automattic that hosts the largest multisite in the world. This is arguably the best place to start blogging if you have never touched WordPress before. https://wordpress.com/ uses “Blog Picture/Icon”
Jetpack uses Site Icon and references favicon.