instant message
US /ˈɪn.stənt ˌmes.ɪdʒ/
UK /ˈɪn.stənt ˌmes.ɪdʒ/

1.
a message sent electronically in real time between two or more users of a computer or mobile device
:
•
I'll send you an instant message with the details.
•
She received an instant message from her friend.