Names Int, Float, Boolean, String, DateTime and ID are reserved and cannot be used to define any other identifiers.
For each type, Dgraph generates a number of GraphQL types needed to operate the GraphQL API, these generated type names also can’t be present in the input schema. For example, for a type Author, Dgraph generates AuthorFilter, AuthorOrderable, AuthorOrder, AuthorRef, AddAuthorInput, UpdateAuthorInput, AuthorPatch, AddAuthorPayload, DeleteAuthorPayload and UpdateAuthorPayload. Thus if Author is present in the input schema, all of those become reserved type names.
This is a companion discussion topic for the original entry at https://dgraph.io/docs/graphql/schema/reserved/