Remember what cars were like in the fifties and sixties? If they went wrong you could lift the bonnet and you could fix most things with a spanner and a screwdriver.
Websites used to be a bit like that. We built each page in html, laying out the content using tables and lists, not very different from writing a document in Word.
But then CMS (content management system) came along. It's great because you can log into your website and manage it yourself. Update your content, run blogs, have forms that interact with the user sending them and you emails, sell stuff the list goes on and on.
There is probably no need to tell you this, but what makes this all work smoothly is very much more involved than websites of old. Not quite so easy to get your spanner out and give the spark plug a clean and blow out the carburettor.
The 'engine' that makes this all possible needs to be kept up to date. Most modern websites rely on numerous extra bits (extensions, widgets etc) to add lots of extra functionality to your website. The core CMS software, Joomla, Wordpress, Drupal or whatever, must be kept up to date. Partly because of the inevitable progress and improvement to the system but more importantly to keep the site as safe as possible.
Each time the core is updated then the extensions that are being used with the website need to be checked to ensure they are still working correctly with the website and are themselves completely up to date. This can be quite a time consuming task, especially if we then find one of the extensions no longer works correctly with the updated website CMS. It happens because the developers of the extension haven't allowed for the changes to the core system. Sometimes when a security issue comes up things have to be updated quickly to ensure there are no security problems. Sometimes this can leave some of the other developers behind. So we have to find a fix to ensure your website is still functioning correctly regardless.