This is a short, relatively non-technical introduction of bitcoin, a
digital currency.  I'm not going to explain the inner workings of the
system other than to say that it based on a form of applied mathematics
known as cryptography.  The system does not depend on a central
authority.

Let's explore the properties of the bitcoin system, assuming it's
mathematical foundations are sound.  First, the number of coins in the
system is fixed.  Over the next twenty-odd years coins will be slowly
created on a pre-determined schedule.  After that time, no new coins can
be created.  Currently about 6 million coins exist.  There will never be
any more than about 21 million coins created.

This fixed schedule of coin creation is one of the properies that makes
bitcoin useful as a currency. People would not like to accept coins as
payment if it was easy for others to create new ones.

Another useful property of bitcoins is that they are easily divisible
into smaller units.  This is a useful property of a currency since it
allows transactions of any value to be completed.

Finally there is property of bitcoins that make it quite unique as a
currency.  The system allows transactions to be made between people at
practically no cost.  To make a transaction, the seller provides the
buyer a special number identifying a digital wallet.  The buyer uses
this number to transfer coins from their wallet to the sellers wallet.
It takes about 10 minutes for this transaction to be cleared by the
system.  After the transaction has cleared it cannot be reversed.