Block

Blocks are zero, one or more instructions, grouped together with or without curly brackets.

A number of commands require blocks of instructions: namespace, use, function, class, trait, interface, enum, closure, switch, match, for, foreach, while, do..while, if-then.

Blocks may require brackets, like for class, switch(), function bodies; they may be optional, like with case, arrow-functions, namespace or loops.

A block may live on its own: it has no impact on the code, although it might be used to arbitrarily group instructions.

<?php

function foo($a) {
    if ($a) {
        $b = 1;
    } else
        $b = 2;

    return $b;
}
?>

Related : Body, Docblock, Bracketless, Curly Brackets