The flex-flow CSS property is a shorthand property that combines both the flex-direction and flex-wrap properties in a single declaration. It allows you to specify the direction of flex items and whether they should wrap onto multiple lines or not. The flex-flow property accepts two values: the flex-direction value followed by the flex-wrap value.
For example, flex-flow: row wrap; sets the flex items to be laid out in a row direction and allows them to wrap onto multiple lines if necessary. It provides a convenient way to control both the direction and wrapping behavior of flex items within a flex container.