a dull reddish-brown color which was originally used for monochrome photographs in the 19th and 20th centuries, or a pigment of this color that is used in watercolors and for monochrome drawings;
e.g. I have a tube of sepia in my box of watercolor paints.
(noun)
a monochromatic photograph or drawing of a reddish-brown to brown color;
e.g. Inside the album, I found a sepia of my grandmother as a child.
(adjective)
having a reddish-brown color, or made using a particular reddish-brown pigment;
e.g. There was a sepia portrait of the old man hanging on the wall.