Sepia or Toning the Prints occurs when you play with the paper and the toner while printing black and white films in the darkroom.
Everybody likes that brown effect in pictures, the same brown effect that makes the exposure older than it actually is. Once you manage to develop your black and white film and get your prints done, don’t exit the darkroom. You can still play and experiment with the toning in them.
Most popular toner is sepia, a technique used to fade the image and give it an older look. Sepia is a two-bath process where you first bleach the print (fades the image), after washing, immersing the print in a toner bath. The image appears with the brown color in it.
By varying the dilution of the toner bath you can control the tones, from a very subtle warming of the image to a deep chocolate brown.