A configuration block that describes an infrastructure object (VM, bucket, database) that Terraform creates and manages. Syntax: resource "type" "local_name" { arguments }.
A Terraform Associate fundamental. Resources have a type (aws_instance, azurerm_resource_group) and a local name (identifier within the code). They're referenced as type.name.attribute. A resource that changes may require recreation (tainted).
Terraform Resource is a concept that can show up on the exam. Check the full guide to see it in context.