The phrase "arbitrage mechanism" refers to a way of making profit by taking advantage of price differences for the same asset in different markets. Full definition
«There is no mentionable arbitrage mechanism, only GBTC shares you can buy / sell are the year - old + [Bitcoin Investment Trust] ones,» one punter wrote on r / BitcoinMarkets. (coindesk.com)
Mutual funds on the other hand, do not have this arbitrage mechanism, so the fund manager is responsible for this continuous buying / selling / re-balancing, hence the hefty transaction fees. (money.stackexchange.com)
When the price of the ETF deviates from the underlying asset value, institutions utilize the arbitrage mechanism afforded by creation units to bring the ETF price back into line with the underlying asset value. (fidelity.com)