It’s also possible to organize events, or chat amongst a group if you have several contacts that all use iMessage.
To set up a group conversation, start a new message, add recipients, and send a text. All replies sent between devices are visible by all members of the group text, as will any subsequent replies within the group message.
To leave an iMessage conversation, open the thread in the Messages app and tap Details. Scroll to the bottom and tap Leave this Conversation and you will no longer get any messages in the thread.
If you don’t want to leave but want to stop receiving notifications, turn on the Do Not Disturb option instead. Return and disable if you do want to receive notifications again.