A Casascius Coin is a type of physical Bitcoin created by Bitcoin enthusiast and hardware maker Mike Caldwell. These coins were first introduced in 2011 and are named after Caldwell's online pseudonym, Casascius.
Each Casascius Coin contains a certain amount of Bitcoin value stored on it, which can be transferred to a digital Bitcoin wallet by using the private key embedded within the coin. This private key is hidden under a tamper-evident holographic sticker on the coin. The physical coin no longer holds any Bitcoin value once the sticker is peeled off and the private key is revealed.
Casascius Coins were made in various denominations of Bitcoin and were often purchased as collector's items or gifts. However, in 2013, Caldwell was forced to stop selling Casascius Coins loaded with digital Bitcoin due to regulatory issues with the U.S. government. Today, unloaded Casascius Coins (without any Bitcoin value) can still be purchased as novelty items.
It's important to note that while Casascius Coins are a physical representation of Bitcoin, Bitcoin itself is a purely digital asset and does not have a physical form.