The term HSS comes from the utilised drill material. High speed steel (HSS) is a high alloy tool steel extremely resistant to wear due to its manufacturing process and is dimensionally stable up to approx. 600°C.
Cutting oil or coolant emulsion should be used as cooling lubricant, when machining steel.
Spirits or petroleum should be used for aluminium.
Normally, plastic and wood can be dry-machined.