If you want to delete your account permanently you will not be able to undelete it after the grace period. You have the option to undelete your account within the grace period of few days if in case you deleted the account by mistake.
If you want to deactivate Facebook account permanently and you never want to re-activate it you can delete the account but don’t forget to get the backup of your account data before deleting the account because it will never be able to undelete and data cannot be retrieved. Its recommended to deactivate the account for few days before you delete it.
You can deactivate your account by following the steps given below:
Then you have to follow the instructions on the screen to confirm your account deactivation request. If you are deactivating your Facebook account it will not be visible to anyone anymore permanently until or unless you reactivate your Facebook account.