Concatenation

Concatenation is the PHP feature that appends two strings together, to make a third, longer one.

Concatenation is also achieved with interpolation, inside a string; by calling echo, multiple times or with multiple arguments; by using the join() function.

Concatenation is done with the dot operator.

<?php
$a = "world";
$b = "Hello ";
echo $b.$a;
// displays Hello world

?>

Documentation

Related : String, Interpolation, Heredocs