Double¶

Double usually means that something is repeated once.

Double is opposed to single, but it may also be distinct with any other number of repetition, such as triple, quadruple, etc.

Things that may be double:

Double quotes "
Double equal ==, not to be confused with the single equal = or the triple one ===
Double colon ::, the static resolution operator
Double plus ++ and minus --, also called plus plus or minus minus, as post-increment and pre-increment operators
Double star **, or exponentiation operator
Double question mark ??, or coalesce operator
Double also refers to float or decimal point numbers.

<?php

    $a = 1;
    $a == 1;  // true
    $a === 1; // true too.

?>