Basically the terms dilute and concentrated are used in reference to the amount of a solute that is dissolved in a given quantity of solvent. In dilute solutions, the amount of solute is less while that of solvent is more. On the other hand in concentrated solutions, the amount of solute is more while that of solvent is less.
For example in concentrated acids there is more amount of acid and less amount of water. The number of H+ ions in such solution is also high. Conversely, dilute acids are those in which amount of acid is less, but water is more. The number of H+ ions in such solutions is low.
also refer Richa Raj Soni