Often times, there is a public subnet included in each regional VPC as well as default routes and access control lists. It is recommended to configure a new VPC with organization-specific settings and security in mind. To learn more about what is included in a default VPC, see the AWS documentation.
References:
https://docs.aws.amazon.com/vpc/latest/userguide/default-vpc.html
AWS accounts created since 2013 have had a default VPC created as well. This is not something that can be removed from AWS altogether, but it can be removed from Terraform resources.
In Terraform -
References:
https://docs.aws.amazon.com/vpc/latest/userguide/default-vpc.html
https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/default_vpc