DNS cache: deletes the DNS cache. The DNS (Domain Name System) translates queries for domain names into IP addresses for the purpose of locating computer services and devices worldwide. Delete this cache if you have problems connecting to the Internet.
Browser cache: deletes the files created when loading Internet pages in the web browser.
Download cache: deletes cache files created when files are downloaded from the web.
Downloaded items list: The URL of each downloaded item is stored in a database. This option deletes the list of all of these URLs.
Browser history: deletes the list of pages that web browsers keep to make pages load more quickly.
Recent searches: removes the recent searches that the web browsers store.
Webpage previews: When you browse the web, Safari creates a preview of each page like an image visible in the Top Sites page, the bookmarks, and the history. You can use this option to remove all these images. When you reopen Safari, a message will propose adding previews from the webpages you’ve visited most recently.
Bookmark icons: Many websites specify an icon (called a favicon) that appears in the Address bar and alongside Bookmarks and addresses in the History menu. This option deletes the icons.
Form values: The info that you type in the forms of websites is saved in a cache. This option deletes the cache.
Cookies: Many websites store small files, named cookies, on your computer, to make return visits easier; for example, it will spare you having to type your name and password when returning to a forum. This option deletes those cookies.
Form values and cookies (may) spare you the typing of user names, passwords, and other required info when you revisit a web-form (as in forums, online-shops, and so on). Warning: Use with caution.