What does the security goal Anonymity (Anonymität) mean?

Keeping the identity of at least one participant in an action unknowable — the action is seen, but not traceable to a person.

An action is anonymous if a participant's identity can't be determined, because they are either:

• not known to the other parties,
• not named (don't appear) to them, or
• acting namelessly within the process.

The point: actions should be observable, but not attributable to a specific person.

Examples:

• Paying cash at a supermarket (no identity attached to the purchase)
• Tor and I2P — designed to hide who the sender and receiver are

Tip: Don't confuse anonymity with confidentiality. Confidentiality hides the content of a message; anonymity hides who sent it. You can have one without the other.

Go deeper:

• Anonymity (Wikipedia) — situations in which the acting person's identity is unknown — the goal defined.
• Tor network (Wikipedia) — onion routing that hides sender and receiver — one of the card's examples.
• I2P (Wikipedia) — an anonymous mix-network layer for peer-to-peer communication — the card's other example.