Mineral oil or Paraffin oil is a useful oil for making oil baths and storing reactive metals. It also has a huge number of uses for the DIY community such as an odorless fuel for certain lamps, rust protection, sealant, lubricant, an inert coolant and many more. It is composed of high boiling inert hydrocarbons distilled from commercial crude oil.
While it is VERY cheap to obtain, sometimes the random DIYer might not find a convenient source. Luckily a very pervasive source available almost everywhere is baby oil. Baby oil is mostly composed of highly purified paraffin oil. It's best to use oil that is unscented and hypoallergenic as that oil is purest and has no reactive additives.