You can read the basics about groups here
Items cannot be hidden or "retired" individually, but you can hide groups. To do this go to the "Home" tab in the ribbon and choose "Preferences". For versions prior to version 11, go to the "View" menu and choose "Preferences".
Then choose the "Groups to Exclude" tab
Any groups checked in this window will be excluded in any searches. The items will still be "active", so if they are used as an ingredient in a recipe or person that is not excluded they will still behave normally.