Which of the following abbreviations refers to a specific type of medication used to treat infections?

C is correct because "ABX" is a common abbreviation used in the medical field to refer to antibiotics, which are specifically designed to treat bacterial infections. Antibiotics work by either killing the bacteria or inhibiting their growth, making them essential in managing a variety of infectious diseases.

In contrast, "ABG," which stands for arterial blood gas, relates to a test that measures the levels of oxygen and carbon dioxide in the blood, rather than a medication. "ALS," or Amyotrophic Lateral Sclerosis, refers to a neurodegenerative disease and not a type of medication. Lastly, "AIDS" stands for Acquired Immunodeficiency Syndrome, which is a condition caused by the human immunodeficiency virus (HIV) and does not denote a specific medication.

Therefore, among the options provided, "ABX" distinctly identifies a category of drugs pivotal in treating infections.