Features are optional WSP (Windows SharePoint) files that can be installed in the SharePoint servers to provide additional functionality. These often provide custom web parts or other desirable customizations.
This can be scoped at the Farm, Web Application, Site Collection, or Web scope.
The original Features were created using SharePoint 2013 and contain references to 2013 file names. This is inconsequential, and the same package is supported on SharePoint 2013, 2016, and 2019 (classic view) environments.
When using the Farm scope, the feature is available in the Central Administration > System Settings > Manage farm features page, and when enabled, code inserted into the entire Farm.
Web Application Scope
When using the Web Application scope, the feature is available in theCentral Administration > Application Management > Manage web applications > Manage Features page, and when enabled, inserted into the fully qualified domain for the specified web application.
Site Collection Scope
When using the Site Collection scope, the feature is available in theSite Collection > Site Settings > Site Collection Administration > Site Collection Features page, and when enabled, inserted into the Site Collection and any sub sites associated with the collection.
When using the Site scope, the feature is available in theSite > Site Settings > Site Actions > Manage site features page, and when enabled, inserted into the just the specified Site. If the site is a Site Collection, sub sites are not automatically tagged.