Final answer:
The term describing the rate of disease transmission in the simple host-pathogen model is βSI, where β is the transmission rate coefficient, and S and I represent the susceptible and infectious populations, respectively.
Step-by-step explanation:
In the simple host-pathogen model, the term that describes the rate of disease transmission is βSI. This term represents the transmission rate coefficient (beta, β) multiplied by the susceptible population (S) and the number of infectious individuals (I). The transmission rate is a crucial aspect in understanding how quickly a disease can spread through a population.