You may have heard the term "Uncommon sat". What is it and why is it special?
A satoshi is the smallest unit of a bitcoin – a bitcoin contains 100 million satoshis. We use Ordinal Theory to number those satoshis, and when they're numbered we call them "Ordinals".
There are many ways we can identify which of these ordinals might be special – perhaps Satoshi Nakamoto themselves held them, or maybe long ago that satoshi was included in the famous "Pizza Transaction". They might be valuable because of where and when they appear on Bitcoin.
Casey Rodarmor, creator of Ordinal Theory, proposed one of the most popular, intuitive ways of identifying special satoshis. It uses natural, pre-programmed events in Bitcoin and says that the "first" satoshi of those events gets a name & rarity. The names for these satoshis are: "Common", "Uncommon", "Rare", "Epic", "Legendary", and "Mythic. Some of us are calling this the "Rodarmor Rarity Index".
Regular satoshis as long as they are not the first sat of the block. 99%+ of all sats are "common"
The first satoshi of a block. A new block is mined approximately every 10 minutes, from now until the end of time.
The first sat of each difficulty adjustment period. Every 2,016 blocks (about 2 weeks) Bitcoin has a "difficulty adjustment".
The first sat of each halving epoch. Every 210,000 blocks (or about every 4 years) Bitcoin has a "Halving event".
The first sat of each "cycle". In Casey Rodarmor's words: "Every six halvings, something magical happens: the halving and the difficulty adjustment coincide. This is called a conjunction, and the time period between conjunctions a cycle. A conjunction occurs roughly every 24 years. The first conjunction should happen some time in 2032."
The first sat of the genesis block, the first satoshi ever created. It is unspendable, unattainable, because Satoshi made the first block unspendable.
Many types of rarities and special satoshi attributes may be determined valuable by the market. Perhaps these "Uncommon" and other satoshis are just the beginning!
All numbers are quoted in 3rd epoch rates, these numbers change during each halving event.