An abiotic factor refers to the non-living components of an ecosystem that affect living organisms, such as temperature, water, sunlight, soil, etc. Based on this definition, the abiotic factor among the options given is "Rainfall." It is a non-living component of the environment and an important abiotic factor that affects various aspects of an ecosystem, including the growth and survival of plants and animals. Rainfall provides the necessary water for plants to grow and for animals to drink, and it affects the distribution of species and the productivity of ecosystems.