What is the best definition for the word influx?

The term "influx" specifically refers to the act of flowing in or an arrival, often in large amounts. It is commonly used in contexts where there is a noticeable increase or surge of something entering a particular place, such as population influx in a city or an influx of donations to a charity. In this context, the word captures the essence of arrivals that lead to significant changes or impacts.

The other terms, such as acceptance, complexity, and theory, do not convey the same meaning of movement or an increase of incoming elements, thus highlighting why arrival fits as the most appropriate definition.