ETFs have a wide range of liquidity. The most popular ETFs are constantly traded, with tens of millions of shares per day changing hands, while others trade only once in a while, even not trading for some days. There are many funds that do not trade very often. The most active ETFs are "very" liquid, with high volume and tight spreads, and the price varies throughout the day. This is in contrast with mutual funds, where all purchases or sales on a given day are executed at the same price at the end of the trading day.