An example of structured data is:

Structured data refers to information that is organized in a predictable format, making it easily searchable and analyzable. This data typically resides in a fixed field within a record or file, commonly in relational databases.

Structured Query Language (SQL) is the standard programming language for managing and manipulating relational databases, which consist of structured data. SQL operates on data that is neatly organized into tables with defined relationships, making it an intrinsic part of handling structured data. The language's capability to query, insert, update, and delete data in structured formats exemplifies its role in working with structured data systems effectively.

In contrast, the other options represent different types of data systems or formats. MongoDB is a NoSQL database that primarily handles unstructured or semi-structured data, while Apache Giraph is a framework for graph processing. JSON, while often used to represent data in a structured manner, is a data interchange format that can also represent unstructured data. Thus, SQL is the most fitting example of a tool that interacts directly with structured data.