Here is one definition of Windows Explorer:
"The graphic interface to the Windows filing system. Using images to represent files and folders, it lets you manage documents by moving them between folders and deleting, copying or renaming them."
RV01 here is a definition of Internet Explorer (Browser):
Definition: " (IE, MSIE) Microsoft's free World-Wide Web browser for Microsoft Windows, Windows 95, Windows NT, and Macintosh. Internet Explorer is the main rival to Netscape Navigator (which runs on many more platforms). Both support the same core features and offer incompatible extensions"
One more definition of Windows Explorer, hope this explains the difference
Explorer
"Also known as Windows Explorer, explorer is used in Microsoft Windows 95 and above to explore and manage the files on the computer drives. Although similar Microsoft Explorer is not the same as "My Computer" and is not the same as "Microsoft Internet Explorer".
Users familiar with earlier version of Windows such as Windows 3.0 or Windows 3.1 can think of explorer being the same thing as file manager."