Shorthand or Ternary Operators

It's commonly referred to as 'shorthand' or the Ternary Operator.

$test = isset($_GET['something']) ? $_GET['something'] : '';
means

if(isset($_GET['something'])) {
    $test = $_GET['something'];
} else {
    $test = '';
}
To break it down:

$test = ... // assign variable
isset(...) // test
? ... // if test is true, do ... (equivalent to if)
: ... // otherwise... (equivalent to else)
Or...

// test --v
if(isset(...)) { // if test is true, do ... (equivalent to ?)
    $test = // assign variable
} else { // otherwise... (equivalent to :)