instant messaging
noun [ U ] uk/ˌɪn.stənt ˈmes.ɪ.dʒɪŋ/ us/ˌɪn.stənt ˈmes.ɪ.dʒɪŋ/
（因特网服务）即时通信
a type of service available on the internet that allows you to exchange written messages with someone else who is using the service at the same time