Interpolation

Interpolation is the PHP feature that automatically replaces variables and public properties by their value in double-quoted strings and Heredoc syntax.

<?php

    $string = "world";

    echo "Hello $string";
    // displays Hello world

?>

Documentation

See also https://www.phpflow.com/php/how-to-use-string-interpolation-in-php/

Related : String, Concatenation, Heredocs, Variables