Final answer:
An antibiotic is a substance produced by a microorganism that inhibits the growth of another microorganism. They can be naturally produced or synthesized in the lab and are essential for treating infections.
Step-by-step explanation:
An antibiotic is any substance produced by a microorganism that is excreted to harm or kill another microorganism. These substances can be naturally produced or synthesized in the laboratory. Antibiotics are important tools for treating and controlling infectious diseases.