Short information about observers
Observer class may be called as a type of Listener class, listening to the events of changes on particular Eloquent Model.
With the command php artisan make:observer --model=ModelName you can create an Observer class that would automatically listen to ModelName (like, "User") events like created(), updated(), etc.
A typical example is updating related records in other DB tables after some change happened in the main related table.
Read more in the official Laravel docs.