Realized capitalization is a variation of market capitalization which values each UTXO based on the price when it was last moved, as opposed to its current value. As such, it represents the realized value of all the coins in the network, as opposed to their market value.
Realized cap reduces the impact of lost coins, and weights coins according to their actual presence in the economy of a given chain.
Realized cap is computed by valuing each UTXO based on the price when it was last moved.
CoinMetrics - Introducing Realized Capitalization