To see if a solution or item is alkaline or not, a ph measurement has to be taken. Water is considered Ph neutral at 7. A ph less than seven is considered acidic and above 7 alkaline. Hydrochloric acid is acidic while hydrogen peroxide is acidic. Hydrochloric is in your household bleach while hydrogen peroxide is in your hair bleach and is also a very good disinfectant in hospital although rarely used now. There is a chemical formula to the calculation of the ph of a solution. This article is not going to go into details about it.
A good example of alkaline in real life is the rechargeable alkaline batteries. The name says it they are alkaline. A rechargeable battery like the ni mh (stands for nickel mercury hydrogen) batteries are cheaper in the long run as they can be used again and again. For that you will need battery chargers of course that can be plugged into power.
Seems we won't be running short of new diets. There is an acid alkaline diet. Proponents of this diet claim that alkaline foods are better for us than acidic ones, since our bodies are slightly alkaline.