Acidophily (from Latin acidus = sour and Ancient Greek philos = friend) refers to the characteristic of organisms in ecology that prefer or require an environment with a low pH value. The pH optimum for growth and reproduction is considered a crucial criterion. Acidophily should be distinguished from acid tolerance. Organisms that can live in environments with low pH values without necessarily preferring them are referred to as acid tolerant. Their pH optimum for growth is therefore higher. The opposite of acidophily is acidophobia.