A lump sum benefit is a benefit taken as a single payment, rather than taken as periodic withdrawals.
Lump sums are only available from unrestricted non-preserved money. Many members in the age group of 55 to 60 have not yet retired and thus have not met a condition of release. Therefore the lump sum option is not available.
Any taxpayer over their preservation age (and retired) pays no tax on lump sums withdrawn from the taxable component that are less than the low rate cap amount of their superannuation account.