What is the name of Apple's built-in instant messaging service?

Apple’s built-in instant messaging service is called iMessage.

Apple introduced iMessage with iOS 5 in 2011 as an internet-based messaging service for Apple devices. It operates through the Messages app, allowing users to send text, photos, videos, documents, locations, and group messages. The service later became available across iPhone, iPad, Mac, Apple Watch, and other Apple platforms.

The app and the service are not exactly the same thing. Messages is Apple’s built-in messaging application, while iMessage is Apple’s own online messaging system inside that app. Messages can also handle carrier-based SMS, MMS, and—on newer software—RCS. That distinction explains why a person can use Messages without every message being an iMessage.

The colored bubbles are a common clue: blue generally indicates an iMessage conversation, while green indicates carrier messaging such as SMS, MMS, or RCS. iMessage conversations support delivery and read receipts, typing indicators, effects, and end-to-end encryption. Unlike Signal, Telegram, or WhatsApp, iMessage is designed primarily for Apple platforms rather than as a cross-platform service.