What is service container in Laravel code example

Example: how to use service container in laravel

use App\Services\Transistor;

$this->app->resolving(Transistor::class, function ($api, $app) {
    // Called when container resolves objects of type "HelpSpot\API"...
});

$this->app->resolving(function ($object, $app) {
    // Called when container resolves object of any type...
});