Lithograph is a miss used word and is used to mean several different things.

 

An original lithograph is when the artist creates the work of art on a stone plate.

 

The word "lithograph" means, "stone print". Lithography works on the simple physical principal that oil and water do not mix. This technique was first used around 1798. Limestone is the most common surface to work on.  The image is drawn in reverse on the stone with greasy crayons. Afterwards, the stone is dampened with water, which is repelled by the greasy medium wherever the artist has drawn. Then the stone is inked with a massive roller loaded with oily ink which adheres to the greasy areas of the design, but is repelled by the wet areas of bare stone. The paper is then pressed to the stone and the ink is transferred to the paper. In a color lithograph, a different stone is used for each color. The stone must be re-inked every time the image is pressed to the paper. Most modern lithographs are signed and numbered to establish an edition.

An offset lithograph, also known as a limited edition print, is a reproduction by a mechanical process, in which the artist has in no way contributed to the process of making an original print: that is, he has not designed the plate. Paintings, drawings, watercolors are photo-mechanically reproduced. Very often the artist signs a number of these "reproductions" but they are not true original lithographs.

You can read more history and details at Lithograph

 

Illustrated is an original lithograph by Marc Chagall, XX Siecle