What is the difference between concentrated and dilute acid?

A concentrated acid vs. a dilute acid.

A concentrated acid is an acid whish is in either pure form or has a high concentration. Laboratory type sulfuric acid (about 98% by weight) is a concentrated strong acid. Strong acid means its pH is close to 0.

A dilute acid is that in which the concentration of the water mixed in the acid is higher than the concentration of the acid itself. If water is added to a strong acid (such as sulfuric acid, mentioned above), the pH (or acidity) of the dilute one would be the same as the concentrated one. Basically a dilute acid just like a concentrated one will completely be ionized in their solution. For instance, 5% sulfuric acid is a dilute acid.