Andreas Pfitzmann and Marit Köhntopp propose a terminology for anonymity, unlinkability, unobservability, and pseudonymity. The terminology aims to provide a precise and expressive language for the field, avoiding the need for researchers to invent their own terms. The terminology is developed in the context of communication networks, where senders send messages to recipients. It can be adapted for other settings, such as database queries or e-commerce. Anonymity is the state of not being identifiable within a set of subjects, known as an anonymity set. The larger and more evenly distributed the anonymity set, the stronger the anonymity. Anonymity sets for senders and recipients may be disjoint, the same, or overlapping. Unlinkability refers to the property that two or more items are no more or less related within a system than they are based on prior knowledge. The probability of items being related remains the same before and after the system's operation. Anonymity can be defined in terms of unlinkability, where the sending and receiving of messages are considered items of interest. Anonymity is then the unlinkability of an item of interest and a subject's identifier. This terminology aims to improve communication and progress in the field by providing a consistent and precise language.Andreas Pfitzmann and Marit Köhntopp propose a terminology for anonymity, unlinkability, unobservability, and pseudonymity. The terminology aims to provide a precise and expressive language for the field, avoiding the need for researchers to invent their own terms. The terminology is developed in the context of communication networks, where senders send messages to recipients. It can be adapted for other settings, such as database queries or e-commerce. Anonymity is the state of not being identifiable within a set of subjects, known as an anonymity set. The larger and more evenly distributed the anonymity set, the stronger the anonymity. Anonymity sets for senders and recipients may be disjoint, the same, or overlapping. Unlinkability refers to the property that two or more items are no more or less related within a system than they are based on prior knowledge. The probability of items being related remains the same before and after the system's operation. Anonymity can be defined in terms of unlinkability, where the sending and receiving of messages are considered items of interest. Anonymity is then the unlinkability of an item of interest and a subject's identifier. This terminology aims to improve communication and progress in the field by providing a consistent and precise language.