Final answer:
The audience described is a Target audience, chosen for their shared interest or purpose. The intended audience affects document reliability by potentially introducing bias. Secondary audiences also need to be considered, as they can influence content interpretation and actions.
Step-by-step explanation:
The type of audience that is a single reader or group of readers with a common purpose is known as a Target audience. This audience is intentionally selected for a particular message, product, or service. The reliability of a document can be affected by the intended audience because the content may be tailored to the audience's beliefs, interests, or level of understanding, possibly introducing bias or a specific viewpoint. Considering the needs and expectations of an audience is essential to effective writing. In some cases, secondary audiences should also be considered, such as people outside of the primary group for whom the document is intended. These readers might have different backgrounds, interests, or requirements, which can influence how a message is interpreted or actions are taken as a result.