The selectItem tag represents a single item in a list of items. Here is the example from Displaying a Menu Using the selectOneMenu Tag:
<h:selectOneMenu
id="shippingOption" required="true"
value="#{cashier.shippingOption}">
<f:selectItem
itemValue="2"
itemLabel="#{bundle.QuickShip}"/>
<f:selectItem
itemValue="5"
itemLabel="#{bundle.NormalShip}"/>
<f:selectItem
itemValue="7"
itemLabel="#{bundle.SaverShip}"/>
</h:selectOneMenu>
The itemValue attribute represents the default value of the SelectItem instance. The itemLabel attribute represents the String that appears in the drop-down menu component on the page.
The itemValue and itemLabel attributes are value-binding-enabled, meaning that they can use value-binding expressions to refer to values in external objects. They can also define literal values, as shown in the example selectOneMenu tag.