What does alkaline mean?
The definition of alkaline
Al”ka*line, a.
Etym: [Cf. F. alcalin.]

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.