What Is PHP? Meaning, Uses and How It Works

PHP is a server-side scripting language for building web pages. A .php file runs on the web server, prints HTML (for example with echo "<h1>Hello</h1>";), and the server sends that HTML to the visitor's browser. The browser never sees the PHP code, only its result.

Press Run: PHP builds the page below, and the Page tab shows it the way a browser would.

<?php
$site = "Corner Bakery";
$items = ["Sourdough" => 4.50, "Croissant" => 2.20, "Rye bread" => 3.80];
?>
<h1>Welcome to <?= $site ?></h1>
<p>Today we have <?= count($items) ?> things in the oven:</p>
<ul>
<?php foreach ($items as $name => $price): ?>
    <li><?= $name ?>: $<?= number_format($price, 2) ?></li>
<?php endforeach; ?>
</ul>

Switch to the Output tab and you see the plain HTML that PHP printed. That text is exactly what a browser would receive. Change a price or add an item and run it again.

What PHP is used for

PHP was made for the web, and that is still where most of it runs:

• Websites and CMSs. WordPress, Drupal and Joomla are written in PHP, and so is every site built on them.
• Web applications. Frameworks such as Laravel and Symfony are used for shops, dashboards, SaaS products and internal tools.
• APIs. A PHP script can print JSON instead of HTML, which is how many mobile apps and JavaScript frontends get their data.
• Command-line scripts. Cron jobs, data imports, report generators and deployment tools run with php script.php, with no web server involved.

<?php
// The same language can answer with JSON, which is what an API does
$product = [
    "id" => 42,
    "name" => "Sourdough",
    "price" => 4.5,
    "inStock" => true,
];

echo json_encode($product, JSON_PRETTY_PRINT);

How a PHP request becomes HTML

When someone opens https://example.com/menu.php, this happens:

1. The browser sends an HTTP request to the server.
2. The web server (Apache, Nginx with PHP-FPM, or PHP's built-in server) sees the .php extension and hands the file to PHP.
3. PHP runs the file from top to bottom. Text outside <?php ... ?> tags is copied to the output as it is; code inside the tags runs and can echo more text.
4. Whatever PHP printed becomes the response body, and the browser renders it.
5. PHP forgets everything. The next request starts a fresh run of the script.

Step 5 is why PHP applications use sessions and databases: nothing in a variable survives between two requests. The form below shows the cycle. Run it, type a name into the form and press Send: the same script runs again, this time with $_POST filled in.

<?php
$name = trim($_POST['name'] ?? '');
?>
<form method="post">
    <label>Your name <input name="name" value="<?= htmlspecialchars($name) ?>"></label>
    <button>Send</button>
</form>

<?php if (($_SERVER['REQUEST_METHOD'] ?? 'GET') === 'POST' && $name !== ''): ?>
    <p>Hello, <?= htmlspecialchars($name) ?>. This page was built by PHP on the server.</p>
<?php else: ?>
    <p>No form data yet. This is the first request.</p>
<?php endif; ?>

htmlspecialchars turns characters like < into <, so a name such as <b>Ada</b> is shown as text instead of becoming markup. Every value that comes from a visitor should be printed this way; the details are on the htmlspecialchars page.

PHP mixes with HTML

A PHP file can be pure code or an HTML page with PHP islands in it. Three tags do almost all the work:

<?php
$hour = 14;
$greeting = $hour < 12 ? "Good morning" : "Good afternoon";
$tasks = ["Order flour", "Clean the oven", "Write the menu"];
?>
<h2><?= $greeting ?></h2>
<p>You have <?= count($tasks) ?> tasks.</p>
<ol>
    <?php foreach ($tasks as $task) { echo "<li>$task</li>"; } ?>
</ol>

Set $hour to 9 and run it again to see the other greeting.

What PHP code looks like

Variables start with $, statements end with ;, and strings in double quotes can contain variables. Arrays work both as lists and as key/value maps.

<?php
function priceWithTax(float $price, float $rate = 0.2): float
{
    return round($price * (1 + $rate), 2);
}

$cart = ["Sourdough" => 4.50, "Croissant" => 2.20];
$total = 0;

foreach ($cart as $item => $price) {
    $total += $price;
    echo "$item: " . priceWithTax($price) . "\n";
}

echo "Total with tax: " . priceWithTax($total) . "\n";

The output is plain text here, because the script prints no HTML tags. That is the same code you would run from a terminal.

Modern PHP (PHP 8)

PHP 8.0 (2020) added match expressions, named arguments, union types, str_contains() and a JIT compiler; PHP 8.1 added enums and readonly properties. Code written for PHP 8.3 looks like this:

<?php
enum Status: string
{
    case Draft = 'draft';
    case Published = 'published';
}

function label(Status $status): string
{
    return match ($status) {
        Status::Draft => 'Not visible yet',
        Status::Published => 'Live on the site',
    };
}

$status = Status::from('published');
echo label($status), "\n";
echo str_contains('php is fun', 'fun') ? "found\n" : "missing\n";

What PHP means

PHP stands for "PHP: Hypertext Preprocessor". The name is recursive: the first P stands for PHP itself. Rasmus Lerdorf released the first version in 1995 as "Personal Home Page Tools", a set of scripts for his own homepage, and the current name arrived with PHP 3 in 1998. "Hypertext preprocessor" describes the job well: PHP processes a file before the hypertext (HTML) is sent.

Common first mistake: opening a .php file in the browser

Double-clicking index.php opens it as a local file, and the browser either shows the raw PHP code or offers to download it. Nothing runs, because there is no PHP on the other end. A .php file has to be served by a web server that passes it to PHP. On your own computer the shortest way is PHP's built-in server:

php -S localhost:8000

Then open http://localhost:8000/index.php. The run PHP page covers this and running scripts from the terminal, and install PHP gets PHP onto your machine first.