Final answer:
An acidic solution is a solution with a low pH number, typically lower than 7.
Step-by-step explanation:
A solution with a low pH number is called an acidic solution. Acidic solutions have a pH lower than 7. The pH of a solution is a measure of its acidity and is determined by the concentration of hydronium ions. As the hydronium ion concentration increases, the pH value decreases, making the solution more acidic.