Differential privacy
Differential privacy is a mathematically-rigorous definition of privacy. An algorithm uses a dataset to calculate its output. An algorithm is said to be differentially private if, based on its output, it is impossible to tell whether or not a particular individual was in the dataset.
In simpler terms, this property is fulfilled if the algorithm's behavior does not noticeably change when a single individual joins or leaves the dataset.[1]
Use cases
Differential privacy is used in data collection on mobile devices. Operators can use this data for learning better models. One example is the keyboard data in Android.[2] Another example is the usage data on iPhone[3]