REGISTRATION in Linguistics: What is it?
We don't speak the same way to a child, a boss, a partner, or a friend. We call this register. It can be more or less formal.
Each person handles their register differently, and this, like the sociolect, technolect, and ecolect, is part of each person's idiolect—that is, the unique way each person speaks, and it identifies us like fingerprints.
This is a fragment of the video "Nobody in the World Speaks Like Me" published on this channel.