Tiffany Glass refers to Favrile glass designed by Louis Comfort Tiffany. Here the glass is infused with variety of brilliant colors. This happens when molten glass is exposed to a series of vapors and metallic oxides, which in turn infuses it with radiant colors and iridescence. It was used in stained glass-windows.         
Tiffany glass was also used to make the glass lamp too and became quite popular too. Thus, often stained leaded glass lamps came to be known as Tiffany lamp, even when not made by Tiffany or his company.