Telling the word processor to not chop the text into parts where you see a new line that YOU have put in.
Framemaker or word?
Yes, as Meow said, "hard returns" contrast with "soft returns".
Many systems, like word processors allow the user to include soft & hard returns.
Hard returns are usually where the user wants a new line. In MsWord, the end of a paragraph is usually where the user presses "Return" putting in a "hard return".
Soft returns are usually where the processor starts a new line because the line is getting full. Some systems allow the user to insert soft returns themselves.
Word processors will sometimes cut the text into pieces, such as for formatting or moving text from page to page. The edges of these pieces, sections or segments is often the end of paragraphs.
Some people use hard returns, that is new lines they put in, for formatting. These will look like paragraphs to the processor & sometimes mean cutting things in half, that should stay together.
This directive "Don't segment on hard returns." probably means do not use the "hard returns" as the edges.