Final answer:
A pathogen is an agent, typically a microorganism, that causes disease in its host. Pathogens include bacteria, viruses, and other infectious agents.
Step-by-step explanation:
The term "pathogen" refers to an agent, usually a microorganism, that causes disease in the organisms that they invade. Pathogens include entities like bacteria, viruses, fungi, protozoa, and parasites. Infectious diseases, such as malaria, African sleeping sickness, and other diseases are caused by these pathogenic agents. In microbiology, the ability to identify and understand pathogens is crucial for diagnosing diseases and for developing treatments like antibiotics and antiviral drugs.