Short answer
WooCommerce is an open-source ecommerce platform for WordPress. It adds product listings, a cart, checkout and order management to a WordPress website. A store also depends on its host, PHP runtime, database, payment services and installed extensions.
Where WooCommerce fits
WooCommerce sits on top of WordPress, which runs on PHP. Payment gateways, shipping tools and accounting integrations extend that stack.
That gives merchants flexibility over how a store works. It also means the platform is more than the WooCommerce plugin alone. An extension can be compatible with WordPress but incompatible with a planned PHP upgrade.
Free software is not a free operating budget
The open-source core does not eliminate hosting, development, paid extensions, payment-processing fees or maintenance. Compare the total work and cost with alternatives, not just the licence price.
The practical question is how closely the platform matches the business. A store with unusual fulfilment rules may value customization. A team seeking minimal technical ownership may prefer a more tightly managed service. What fits one business may not fit another.
What matters during an update
A homepage loading is weak evidence that a store works. Test product variations, tax and shipping calculations, checkout, payment confirmation, order emails and stock changes. Use test payment modes when available and control outgoing messages in staging.
The official server recommendations describe the current hosting requirements. Check them against the exact store and extension versions; do not assume the newest PHP branch is already validated by every integration.
A PHP upgrade rotates the runtime under all of that, so plan a rollback path and test in staging first. Magento is another PHP-based commerce option, but moving platforms is a separate business decision from fixing an outdated runtime.