QuickType

QuickType is a predictive text application that uses natural language processing and machine learning to improve its  accuracy and usefulness.

QuickType, which was introduced in iOS 8, is like an advanced version of auto-correct or auto-complete software. It is designed to make the soft keyboards on Apple mobile devices more user-friendly by gathering and analyzing text whenever the end user types in a blank field. The application learns from the data it collects, so it is able to more accurately target recommendations to specific email recipients, phone contacts, SMS contacts or web sites. 

The goal of the application is to convincingly emulate the user's natural language in different contexts. QuickType can even learn and imitate the different speech patterns an end user employs with different people, recommending “TY” for “thank you” or “CU soon” for “see you soon” once a precedent has been set. The software can even recommend full sentences when it recognizes an appropriate context and will learn to suggest full-sentence responses to incoming texts or email messages.

See an introduction to QuickType:

See also: auto-correct fail, Cupertino effect