Display is one of those. When display is off it means you are ignoring the person. You can control display using the /ignore and /unignore commands.
The /show display command tells you who you are ignoring.
- ... Technically, display is a degree value, so we could not only control ignore or highlighting levels of a person like this. One day we may want to combine the display value mathematically with the amount of importance (or trust) you give to the context in which you received a message from this person. An in-between display value would then result in this person's talk not being displayed for an unimportant chit-chat chatroom whereas it is still displayed in an important announcement forum.
The /cancel command lets you delete the entire record for a peer.