0 to communicate with someone over the internet using a service available on the internet that allows you to exchange written messages with someone else who is using the service at the same time
1 IM
2 a written message that can be sent over the internet to someone who is using the internet at the same time:
This software translates foreign-language instant messages.
3 to use the internet to exchange written messages very quickly with someone who is using the internet at the same time:
