a measurement of the level of acid or alkali in a solution or substance. In the pH range of 0 to 14 a reading of below 7 shows an acid and of above 7 shows an alkali. pH 值（溶液或物质的酸碱度。pH 值介于 0 至 14，7 以下为酸，7 以上为碱） a pH of 7.5 pH 值 7.5 to test the pH level of the soil 测试土壤的酸碱度
Word Originearly 20th cent.: from p representing German Potenz ‘power’ + H, the symbol for hydrogen.