What does "alkaline" mean?

Alkaline: Of or pertaining to an alkali or to alkalies; having the properties of an alkali. Alkaline earths, certain substances, as lime, baryta, strontia, and magnesia, possessing some of the qualities of alkalies. -- Alkaline metals, potassium, sodium, cæsium, lithium, rubidium. -- Alkaline reaction, a reaction indicating alkalinity, as by the action on limits, turmeric, etc.