An antibiotic is a type of medication designed to kill or inhibit the growth of bacteria, thereby treating bacterial infections. They work by targeting specific bacterial functions or structures, such as the bacterial cell wall, protein synthesis, or DNA replication. However, antibiotics are ineffective against viral infections. The inappropriate or overuse of antibiotics can lead to antibiotic resistance, where bacteria evolve to survive despite the presence of these drugs, posing a significant challenge to modern medicine.