Sentence:  Citizens of the <WSD>United</WSD> States who , on April 15 , are not in the United States or Puerto Rico , are allowed an extension of time until June 15 for filing the return for the preceding calendar year . 
Meaning of the word marked with <WSD> tags:  North American republic containing 50 states - 48 conterminous states in North America plus Alaska in northwest North America and the Hawaiian Islands in the Pacific Ocean; achieved independence in 1776