Hook: definition
A hook is a specific point in PrestaShop's code where a module can run its own logic, without touching the core files.
What a hook is for
PrestaShop fires dozens of hooks at specific moments: header rendering, a product added to the cart, an order validated, footer rendering. A module attaches to one by calling registerHook() on install, then implementing a method named after the hook, for example hookDisplayHeader to insert a tag into the <head>, or hookActionValidateOrder to react to every validated order.
This mechanism avoids modifying PrestaShop's native files. For an online seller, it's what guarantees that a feature added by a module keeps working after a shop update, as long as the hook still exists in the target version.
The downside shows up when several modules attach to the same hook: their execution order, adjustable in the back office, can cause visual conflicts if two modules inject content in the same spot.
Frequently asked questions
Can a hook be added to a page that doesn't offer one?
Why does an installed module show nothing on the shop?
Is it risky to edit a hookXxx method in a third-party module?
Describe your need in one minute
A few targeted questions so I can reply with an estimate rather than another questionnaire.