'XML elements are declared with an element declaration. An element declaration has
the following syntax:
<!ELEMENT element-name category>
<!ELEMENT element-name (element-content)>
Here, category can be EMPTY or ANY. EMPTY
I have not understood what they exactly meant by it. Any suggestions, ideas, links, resources highly appreciated. Thanks in advance
The document you're reading is describing the syntax of a DTD, a "Document Type Definition", a somewhat outdated method for describing XML documents. The example is a rather literal example of what the allowed content would look like.
Neither DTDs nor XML itself have anything to do with Java, so your title "Java element" is confusing! I'm going to move this thread to our XML forum; feel free to ask followup questions.