Creation Unit

What Does Creation Unit Mean?
A set of shares or securities that makes up one unit of a fund held by the trust that underlies an exchange-traded fund (ETF). One creation unit is the denomination of underlying assets that can be redeemed for a certain number of ETF shares.

Investopedia explains Creation Unit
Creation units can vary in size; with most containing between 25,000 and 600,000 ETF shares each. The use of creation units in the construction of ETF shares is critical because they allow for the representation of the underlying assets - the ETF shares, which represent a tiny chunk of a creation share - to be traded intraday. The ability to trade ETFs on an exchange gives them a significant advantage over comparable investment vehicles, such as mutual funds.