The text only looks like Latin, but actually means nothing, yet is sufficiently like ordinary text to demonstrate a font without distracting the reader - that at least is the theory. It loosely approximates the frequency with which letters occur in English, which is why at first glance it looks realistic. The letters and letter spacing in Lorem ipsum display the weight, design, and other important features of a typeface.
What is really extraordinary is that this fake Latin has been used by the printing industry as standard dummy text ever since the 1500s. In those years some anonymous typesetter took a galley of type - of proper Latin - and jumbled it to make a book of type samples.
It has survived almost 500 years of traditional typesetting all the way into the electronic era and is widely used in the preliminary design of web sites, brochures and magazines.
Oddly enough, the graphic design, putting in nonsense filler copy is known as "greeking" - not latining - presumably because of the phrase "it's all Greek to me." In the pre-computer design era, the Letraset company produced Lorem ipsum on adhesive sheets in different sizes and typefaces.
But what of that original Latin that the unknown printer scrambled long ago? Surprisingly, we do know what it was, thans to Richard McClintock, a former Latin professor turned publications director at Hampden-Sydney College in Virginia. Growing curious about the words meant, McClintock looked up one likely one - "consectetur" (there's no Latin word lorem) - in a Latin dictionary. He went through citations of its use in classical literature until he found one that seemed to have a familiar context.
The Lorem ipsum paragraphs are the jumbled remnants of a passage from the classical Roma writer Cicero that begins: "Neque porro quisquam est qui dolorem ipsum quia dolor sit amet, consectetur, adipisci velit..."
(There is no one who loves pain itself, who seeks it out, or wants to have it, simply because it is pain.)
It is from De Finibus Bonorum et Malorum (Sec. 1.10.32). It is a treatise on the theory of ethics, written in 45 BCE, and it became very popular during the Renaissance.
Footnote: Magnum lorem borem