Which of these describes steganography?

Steganography is fundamentally about concealing the existence of information rather than just hiding the content itself. Specifically, it involves embedding hidden data within other non-sensitive data, effectively making it undetectable to any observer who is not aware of the hidden information. This technique can be particularly useful for protecting sensitive communications because it allows the sender to communicate without revealing that a communication is taking place at all.

In contrast, options such as making data unreadable, ensuring data integrity, or encrypting data using keys focus on techniques that either make data inaccessible or alter its state to prove authenticity, but they do not address the specific aim of steganography, which is to mask the existence of the data itself. Therefore, the description that highlights the aspect of concealing the fact that sensitive information is being communicated accurately captures the essence of steganography.