Pathogen - A biological agent that causes disease.⏎
Organism - A living being that can reproduce, grow, react to external stimuli, and maintain its internal equilibrium.⏎
Pandemic - An increase in the occurrence of a particular disease over a very large region, such as a continent or the entire globe, that is greater than what is expected over a given period of time.⏎
Peptic Ulcer - An open sore that develops on the inner lining of the stomach or upper small intestine.⏎