Use

The use operator has three distinct usage.

The use operator allows the import and aliasing of fully qualified names (such as classes, interfaces, constants, …) in the current namespace.

When use used inside a class or a trait, it imports a trait and its methods and properties.

When use is used with a closure, it imports the listed variables in the closure, from the defining environment.

<?php

namespace \My\Space {
    // class importation with use
    use \Some\Other\Space\aClass as A;

    class B {
        // trait importation of use
        use MyTrait;

        function foo() {
            $a = 1;
            // use imports the variable $a in the closure. Its value is accessible at execution time.
            $closure = function ($b) use ($a) { return $a + $b;}
        }
    }
    // class importation with use
    use \Some\Other\Space\aClass as A;

}

?>

Documentation

Related : Fully Qualified Name, Use Alias, Closure, Traits, Fully Qualified Name