type and token
In the study of texts, the ratio of the number of different words, called types, to the total number of words, called tokens. For example, in a particular text, the number of different words may be 1,000 and the total number of words 5,000, because common words such as the may occur several times, and in this case the type-token ratio would be 1/5 or 0.2. See token (3). See also stylostatistics. TTR abbrev.