Market cap values every coin at today's price, including coins that haven't moved in a decade. Realised cap values each coin at the price when it last moved, so it adds up what the market has actually paid.
A worked example
An example chain with four coins (made-up numbers)
Coins
Price when last moved
Realised value
1
$20,000
$20,000
2
$30,000
$60,000
1
$60,000
$60,000
4
$140,000
Realised cap is $140,000 and realised price is that divided by the coins: $35,000. If the market price is $50,000, the average coin sits on a paper gain of about 43%.
How to read it
Treat realised price as the market's average cost. When price trades well above it, most holders are in profit and some will sell. When price falls below it, the average holder is under water, which has only happened in deep bear markets, and those stretches have historically been good times to be paying attention rather than selling.
It isn't a perfect cost basis. A coin that moves between someone's own wallets gets a new "cost" with no sale at all, and lost coins hold their old price for ever. Entity-adjusted versions remove some of the first problem, at the cost of depending on clustering.
