In chemistry, any aqueous solution can be classified as belonging to one of three groups: acidic, basic, or neutral solutions.
Acidic Solution Definition
An acidic solution is any aqueous solution which has a pH < 7.0 ([H+] > 1.0 x 10-7 M). An aqueous solution is one which has water as its solvent. While it's never a good idea to taste an unknown solution, acidic solutions are sour, in contrast to alkaline solutions, which are soapy.
Examples: Lemon juice, vinegar, 0.1 M HCl, or any concentration of an acid in water are examples of acidic solutions.