The ledger type can relate to Private or Public data. So a full public ledger and public transactions, or private ledgers and private transactions. So just like the data types we have, the ledger can apply to any and give people the ability for public and private ledgers.
Hope that helps.
[edit, you can also use the ledger flag on a data type for a single transaction, so for instance to keep a “receipt” of a safecoin payment etc. ]