On an item's page choose More → Move to trash…. To trash several, select them in Holdings and choose Trash… (see Selecting many items).
A trashed item leaves your catalog, totals, reports and exports, but its history, photos and documents are kept. A toast offers Undo straight away.
Restoring
Open Settings → Trash and choose Restore beside the item. Items stay there for 30 days, then are deleted for good.
Deleting for good
Delete for good beside an item, or Empty trash, removes it from the vault immediately — its record, history, and any photos or documents nothing else uses. This cannot be undone, though backups made before then still contain it.