A Tayden is the basic monetary unit of currency that is used by the aliens in Undertown and the known universe.
A tayden is a small piece of Taydenite that is shaped like a gemstone and has a symbol on it.
It has not yet been specified as to how much a tayden is worth, though its value is significant, being made of Taydenite.
However, in Clyde Five, Liam spoke of 6 taydens as if it were an insignificant amount. The Sock Vendor also seemed to share this opinion.
In Have I Got a Deal for You, Professor Hokestar mentioned his Miracle Elixir costs two taydens a bottle.
In Hot Stretch, Ben used a tayden to buy a bottle of water, while an old thermoelectric generator was on sale for 12 taydens.
In Many Happy Returns, Ben scattered some taydens for Y-it.
In Special Delivery, Ben received varying amounts of taydens for his deliveries.
In Clyde Five, Liam robbed Sock Vendor's shop's safe, which contained 6 taydens.
In Universe vs. Tennyson, apparently the fine for re-creating the Universe is 5 taydens.
In The Color of Monkey, one tayden purchased a cup of artificial Tiffin-flavored ice cream.