Installation
Installation covers two distinct things that share a name but happen at different layers.
PHP installation is the process of getting the PHP runtime itself onto a machine so that any PHP script can be executed at all. Depending on the platform and the intended use, this can mean installing a prebuilt package through an operating system’s package manager, such as apt on Debian and Ubuntu, dnf on Fedora, or Homebrew on macOS; downloading official prebuilt binaries for Windows; running an all-in-one local development stack such as XAMPP, MAMP, or WAMP that bundles PHP with a web server and a database; pulling an official php Docker image for containerized environments; or compiling PHP from source with ./configure, make, and make install for full control over which extensions and build flags are enabled. It is typically followed by configuring php.ini to enable the required extensions and set runtime directives, and verified by running php -v from the command line or checking the output of phpinfo() through a web server. Multiple PHP versions can coexist on the same machine using version managers or separate installation prefixes, which is common when maintaining several projects with different version requirements. This step is done once per machine, or once per PHP version on that machine.
PHP application installation, by contrast, assumes the runtime already exists and instead sets up one particular application or library written in PHP so that it becomes usable. For a library, this usually means composer install, which reads composer.json and downloads the declared dependencies into vendor/. For a full application such as WordPress, Drupal, or a bespoke project, it typically also involves creating a configuration file, initializing a database schema, and setting file and directory permissions, often walked through by a first-run install wizard in the browser or a documented sequence of console commands. Application installation is repeated for every project and every environment, and is a separate concern from deploy, which is about publishing an already-installed application to a live server.