Andreas Pfitzmann and Marit Köhntopp propose a set of precise and expressive terminology for the field of privacy and anonymity, including *anonymity*, *unlinkability*, *unobservability*, and *pseudonymity*. They define these terms within a communication network setting where senders and recipients communicate using messages. The attacker, who may monitor or manipulate the communication, cannot obtain information about the sender or recipient from the message content. - **Anonymity**: A subject is anonymous within a set of subjects if they cannot be identified within that set. The anonymity set includes all possible subjects who might cause an action. Anonymity is stronger when the anonymity set is larger and the distribution of subjects within it is more even. - **Unlinkability**: Two or more items are unlinkable if their relationship within the system remains the same before and after the run, as perceived by the attacker. For example, two messages are unlinkable if the probability that they are sent by the same sender and/or received by the same recipient remains the same before and after the communication. - **Anonymity in Terms of Unlinkability**: Anonymity can be defined as the unlinkability of an item of interest (IOI) and an identifier of a subject (ID). Specifically, the anonymity of an IOI is the unlinkability of the IOI and its identifier. The authors aim to standardize the terminology to facilitate better progress in the field by avoiding the reinvention of language by individual researchers.Andreas Pfitzmann and Marit Köhntopp propose a set of precise and expressive terminology for the field of privacy and anonymity, including *anonymity*, *unlinkability*, *unobservability*, and *pseudonymity*. They define these terms within a communication network setting where senders and recipients communicate using messages. The attacker, who may monitor or manipulate the communication, cannot obtain information about the sender or recipient from the message content. - **Anonymity**: A subject is anonymous within a set of subjects if they cannot be identified within that set. The anonymity set includes all possible subjects who might cause an action. Anonymity is stronger when the anonymity set is larger and the distribution of subjects within it is more even. - **Unlinkability**: Two or more items are unlinkable if their relationship within the system remains the same before and after the run, as perceived by the attacker. For example, two messages are unlinkable if the probability that they are sent by the same sender and/or received by the same recipient remains the same before and after the communication. - **Anonymity in Terms of Unlinkability**: Anonymity can be defined as the unlinkability of an item of interest (IOI) and an identifier of a subject (ID). Specifically, the anonymity of an IOI is the unlinkability of the IOI and its identifier. The authors aim to standardize the terminology to facilitate better progress in the field by avoiding the reinvention of language by individual researchers.