What does the protection goal Availability (Verfügbarkeit) guarantee?

That services or information can be accessed within the time the user needs them.

Availability is about timely access. It's threatened by:

• Denial-of-Service / DDoS attacks
• Hardware failure, power/network outages
• Ransomware (encrypting files makes them unavailable)
• Force majeure (fire, flood)

It's defended with redundancy, backups, failover, capacity planning, and DDoS mitigation.

Tip: Availability is the goal whose violation is noticed immediately — when a system is down, everyone knows. Contrast that with confidentiality breaches, which can stay hidden for years.