Total number of unspent transparent transaction outputs (UTXOs) over time. Computed as the cumulative difference between outputs created and inputs spent. A growing UTXO set means more unspent outputs exist — more addresses holding coins. A shrinking set means consolidation. This is a measure of the transparent address space complexity.
A UTXO is one unspent output. One wallet can hold hundreds; one output can hold any amount. So this counts pieces, and a rise means the transparent set is more fragmented — not that more people arrived and not that more value did.
The level is a stock. It grows when more outputs are created than spent and shrinks on consolidation — a wallet sweeping many small outputs into one makes the set fall while holding exactly the same ZEC.
It is a proxy for transparent-layer activity that ignores value entirely, which is its point: a chain-wide consolidation and a wave of new small holders look identical on transaction counts and opposite here.