An abbreviation of "messenger app"; an app for sending/receiving messages and making calls. Often used in casual or shortened written forms.
友達に『メッセアプリで連絡して』と言われた。
A friend told me, 'Contact me via the messenger app.'
会議の招集はメッセアプリのグループで共有します。
Meeting invitations will be shared in the messenger app group.