A type of ink pen, currently popular. Gel ink is supposed to be more smooth-flowing coming out of the ballpoint or rollerball end of the pen, and waterproof. The ink is also more opaque, allowing for metallic or pastel-colored inks that will show up on dark paper (but not all gel inks do this). Sakura's Gelly Roll, Pentel's Milky and several other manufacturers' lines are not too hard to find.