TTR, or Text-to-Text Ratio, is a measure of the diversity and complexity of language used in a written text. It calculates the ratio of unique words to the total number of words in a text, providing insight into the richness and variety of vocabulary used. A high TTR indicates a more diverse and sophisticated use of language, while a low TTR suggests a more repetitive and simplistic writing style. TTR is commonly used in linguistics, education, and writing analysis to assess the level of difficulty and effectiveness of written communication.