T9, or Text on 9 keys, is a predictive text technology designed for mobile phones. It simplifies typing by predicting words based on the number of key presses. Each number on a phone keypad corresponds to multiple letters, and T9 uses a built-in dictionary to guess the intended word, making texting faster and easier. Developed in the 1990s, T9 became popular before the rise of touchscreen smartphones. It was especially useful for users of feature phones, allowing them to send messages without needing to press each key multiple times. T9 significantly improved texting efficiency during its time.