This feature of magento can be used for adding text to your magento store. Custom variables are moveable pieces of plain text or HTML content great for adding to transactional emails, or adding constant copy and designs to your store with Static Blocks and CMS pages in magento. You can use this tool to make your client’s life easier who will handling the magento admin.
Go to System -> Custom Variables and click on Add New variable. Enter code and text.
After you can go to any cms page or block. Its will be available in insert variables section of WYSIWYG.