What is the difference between ‘key variables’ and ‘keys’?

Key variables are your indirect identifiers that are most likely to lead to a disclosure whereas keys are all the unique combinations of values those indirect identifiers take. For the key variables ‘Marital Status’ and ‘Gender’ you could have keys such as ‘Married, Female’, ‘Married, Male’ and ‘Single, Female’. The number of times, or the frequency, a given key appears in a dataset is the basis for many disclosure risk measures.