predictive text

Short definition from Wiktionary

Noun

1. 1
   A system for inputting text on a device where individual buttons correspond to several characters that attempts to guess which word was intended (typically out of a writable vocabulary), as opposed to a system where disambiguation is achieved through repeated presses of the same key.
2. 2
   A system, as in a word processor, that attempts to predict and autocomplete the text being typed.