Solutions can vary widely in terms of how much of the dissolved substance is actually present.
A very dilute acid solution has very little acid and may not be harmful or even noticeably acidic. Since acids and bases neutralize each other, and indicators can show if a solution is acid or basic, we can compare volumes added to see how concentrated a solution is. Add 10 drops of ammonia solution to an indicator solution. If you don't stir as you add the vinegar, different portions of the solution will be different colors. Note what happens when you do stir.