Frogleg wrote:

What *does* the "5% acidity" label on a bottle of kitchen vinegar mean
anyhow? 5% the strength of pure hydrochloric acid?

Acetic acid. ;-)

In Germany you can buy a product called "vinegar essence" which is
something like 20% acetic acid. Some people water it down and use it for
salad dressings. Others clean the kitchen floor with it