What is a hard return?

A hard return is an actual symbol inserted into the text. The hard-return symbol is usually invisible, but most word processors support a mode that lets you see them. Whenever you press the Return or Enter key while editing a document, the word processor inserts a hard return. 

Hard returns cause the word processor to start a new line regardless of how margins are set. Therefore, if a document contains hard returns, the lines will end at the same place even if you change the margins.