The words concentrated and dilute describe how much acid is dissolved in the water. They are about the amount of substance. A concentrated acid has a large amount of acid in a given volume of solution. A dilute acid has a small amount of acid in the same volume. Concentration is often measured in mol/dm3, which is the amount of acid in moles in each cubic decimetre of solution. Adding water to an acid makes it more dilute.
The words strong and weak describe something different, the degree of ionisation. When an acid dissolves in water its molecules can split up to release hydrogen ions, H+. A strong acid is completely ionised in water, so every molecule releases a hydrogen ion. Hydrochloric acid, nitric acid and sulfuric acid are strong acids. A weak acid is only partly ionised, so most of its molecules stay as they are and only a few release hydrogen ions. Ethanoic acid, citric acid and carbonic acid are weak acids.
The two ideas are independent. You can have a concentrated solution of a weak acid, and a dilute solution of a strong acid. Concentration tells you how much acid is dissolved. Strength tells you what fraction of it has ionised.
