Inoculum refers to a substance containing microorganisms, such as bacteria or fungi, used to initiate fermentation or infection in a host. It is commonly used in various fields, including microbiology, agriculture, and medicine, to promote growth or study the effects of specific organisms. Inoculum can be derived from natural sources or produced in laboratories. In agriculture, it is often used to enhance soil health or crop yields by introducing beneficial microbes. In medicine, inoculum plays a crucial role in vaccines, where it helps stimulate the immune response against diseases caused by pathogens like viruses or bacteria.