A writing utensil containing "gel" ink, which resembles a liquidy paint that can be applied to almost any surface and comes in every possible color you can imagine from metallic orange, to sparkly purple, to glow-in-the-dark green. This newest and greatest pen technology is comfortable to use because it requires little hand pressure, but often the ink takes a bit long to dry.
Gel pen manufacturers include: Marvy, Sanford, Zebra, Pilot, and Sakura.
Signing my mortgage was so much more fun with a iridescent blue gel pen.
Any true pen slut owns at least ten different gel pens.