Golf
Code golf is about creating the shortest code, in bytes, to solve a given problem, in a specific language or free of choice. Solutions are scored purely on character count; readability, style, and maintainability are deliberately ignored.
PHP golfers exploit language-specific shortcuts to shave bytes: the short echo tag <?=, omitting the closing ?> tag, the null coalescing and null coalescing assignment operators, ?? and ??=, instead of isset() checks, the ternary shorthand ?:, list()/[] destructuring instead of separate assignments, loose == comparisons, and string-to-number juggling such as writing "1e9" instead of 1000000000.
Community sites such as Code Golf Stack Exchange and Anarchy Golf host PHP-specific challenges, and submissions are usually scored with strlen() run on the minified source.
<?php
// All spaces are removed to make the code compact
$billionPlusOne=1+1e9;
// 1e9 is cast automatically to 1000000000 or 1_000_000_000, but takes less space to write
?>