Batch Item Editor edits many items of a module on one screen: blog posts, audio files, members and so on. Use it to fix one field on dozens of items, or to delete many items at once.
ACP > Modules > Admin > Batch Item Editor
It has no settings. When it's active, every module that stores items gets a Batch Edit Items tool on its Tools tab. For example: ACP > Modules > Profile > Blog > Tools > Batch Edit Items. Only master admins can use it.
Changes are saved straight to the items, with no undo. Deleted items are gone, together with their files. Make a backup first if you're changing a lot: see DB and System Backup.