Which of the following best describes the concept of 'Availability' in information security?

The concept of 'Availability' in information security refers specifically to ensuring that information is accessible and usable when required by authorized users. This means that systems, applications, and services need to be operational and maintain their functionality so that end-users can obtain the data they need without delays or failures. It encompasses aspects such as system uptime, redundancy, and uninterrupted access to resources.

The other options relate to different aspects of information security: keeping information secret is associated with confidentiality, preventing unauthorized data changes relates to integrity, and ensuring data encryption is a measure aimed primarily at securing data during transmission or storage. However, none of these options address the core principle of ensuring timely access to information, which is why the second choice is the most accurate description of 'Availability' in the context of information security.