An antibacterial substance or compound is one that kills or inhibits the growth of bacteria. These can include antibiotics, such as penicillin or erythromycin, which target specific bacterial processes to prevent their growth or survival. Other examples include disinfectants like bleach or alcohol, which are used to kill bacteria on surfaces. Additionally, certain natural compounds like tea tree oil or garlic extract possess antibacterial properties. These substances work by disrupting bacterial cell membranes, interfering with their metabolism, or targeting specific proteins essential for bacterial survival.