Which of the following best describes plaintext?

Plaintext refers to information that is formatted in a way that is easily readable by humans, without any encoding or encryption applied to it. This means that the content can be understood directly without requiring any special tools or keys for decryption. Typically, plaintext can include regular text files, messages, or documents that contain understandable data such as letters, numbers, or symbols in their original form.

The other options describe different concepts: encrypted text refers to data that has been transformed to prevent unauthorized access; a format designed for high-security messages relates to protocols used to secure data rather than the readable form itself; and a protocol for file attachments pertains to methods for sending files over networks. Understanding the definition of plaintext as human-readable information is fundamental in topics related to data security and encryption concepts.