The term COMPOUND WITH A LOW PH is referring to an ACID, which is a type of compound that has a low pH. An ACID is a substance that releases hydrogen ions when dissolved in water, and has a pH lower than 7. Acids are often used in industrial processes, such as in the production of fertilizers, and can also be found in everyday items like vinegar and lemon juice. The crossword solution for this term is ACID, which is a four-letter word.