Extended Templating Kit
Extended Templating Kit (ETK) is a Magnolia CMS module that extends the Standard Templating Kit. It provides multisite support for managing multiple websites in a single Magnolia instance. Each site has its own site definition, templates, themes, domains and locales.
Extended Templating Kit is an Enterprise Edition module. It is typically already installed. Go to Magnolia Store > Installed modules in AdminCentral to check.
See the general module uninstalling instructions and advice.