List of Widget Zones - 4.x

FYI, you can now, as of 4.10, easily get the list of public widget zones from the source code
https://github.com/nopSolutions/nopCommerce/blob/eda3a16ed7f3bc6caad0182a44437fc9dbbc5319/src/Presentation/Nop.Web.Framework/Infrastructure/PublicWidgetZones.cs

Are there any definitions of the widget zones available? Some of them are a bit cryptic, like "Content after" and "Main column before".

To see where widget zones are being used, you'd have to search for them in the .cshtml files.  E.g. ContentAfter

\Nop.Web\Views\Shared\_Root.cshtml

    <div class="master-wrapper-content">
        @await Component.InvokeAsync("Widget", new { widgetZone = PublicWidgetZones.ContentBefore })
[...]
        @await Component.InvokeAsync("Widget", new { widgetZone = PublicWidgetZones.ContentAfter })
    </div>