Focus Mode is a feature that was designed to allow iPhone users to focus on tasks by muting and hiding notifications, messages, phone calls, and other alerts on their devices. The Focus feature used to be very simple and called Do Not Disturb Mode, but with later versions of iOS, Apple added a bunch of complexity to Focus Modes that cause some users confusion, not only about using the feature in general, but particularly regarding how to disable Focus Modes or how to get out of and escape Focus Modes.
You can often tell if someone is on Focus Mode because calling their iPhone will result in going directly to voicemail, and if you message them it may say something like “[Name] has notifications silenced.”