Budgets allow the user to get notified when costs or usage exceed a certain predefined amount.

You define what you want to track ( just cost, service usage or utilisation of saving plans and reserved instances ), the amount and the scope (all resources in the account or specific projects/services)

Then you define a threshold and the target of your Budget Notification ( email, SNS topic or ChatBot). You can also define a Budget Action to be triggered (like stopping EC2/RDS instances or changing IAM Permissions or SCPs).

Finally Budget Reports can be exported to have an overview of all your budgets and their status.