acids and bases

What makes an acid an acid?  Well after I was asked this question and I went online and looked up what the definition of an acid was.  Well the term acid comes from the Latin word acere which means sour.  It named a couple of acids and one of them was vinegar which we used in our lab recently.  See in our experiment we mixed acids and bases.  What we did was take the vinegar which is the acid and the tablets which is the bases.  See when the bases are mixed with the acids it becomes less and less of an acid as the article said that i read.  That's exactly what happened in this experiment we did.  When we took the Ph of the  vinegar in the beginning it showed that it was an acid well the numbers changed once we added the tablets so instead of it staying an acid it changed into more of a base.