Instant messaging is a form of written communication that allows you to send messages from one computer to another. The message appears immediately on the screen of the computer you send it to, provided the computer is using the service. The abbreviation IM is also used.
They keep in contact through instant messaging.
instant messaging in British English
noun
computing
the online facility that allows the instant exchange of written messages between two or more people using different computers or mobile phones
Abbreviation: IM
instant messaging in American English
an online service enabling subscribers to chat1 (sense 2) with one another