What does "Reserved" indicate on Financial Types/Accounts?
'Reserved' on items like this in Civi indicates that it's something that you don't want to be updated or deleted, as it's an important item.  So non-admin people can't update or delete it - in this case you have to have the 'CiviContribute: access CiviContribute' permission to be able to update.  Groups and tags can be protected in a similar way.