Magento 2.1.x Notice: Magento 2.1.18 is the final 2.1.x release. After June 2019, Magento 2.1.x will no longer receive security patches, quality fixes, or documentation updates. To maintain your site's performance, security, and PCIPayment Card Industry: Refers to debit and credit cards and their associated businesses. compliance, upgrade to the latest version of Magento. The Magento User Guide 2.1.x remains available in PDF for Open Source and Commerce.
A themeA package that contains graphics and appearance information, and customizes the look and feel of the store. is a collection of files that determines the visual presentation of your store. When you first install Magento Open Source, the design elements of the store are based on the “Default” Theme. In addition to the initial default theme that comes with your Magento installation, there is a wide variety of themes that are available “off the shelf” on Magento Connect.