Unstructured data refers to data that does not have a pre-defined data model or schema. Examples include text, images, audio, and video files. Call center transcripts are unstructured data because they are composed of free-form text, which does not follow a specific schema or structure.
Option D: Call center transcripts is correct because it represents unstructured data, as opposed to structured data like customer orders or product ratings.
[References:, Google Cloud: Understanding Unstructured Data, Google Cloud Storage Solutions: Managing Unstructured Data, ]