Intelligence is the ability of an agent to make decisions and execute complex tasks.

For example, suppose I release a housefly into a room that contains both a nice stinky dog turd, and an inert block of wood. If the fly heads towards the shit, it made an intelligent decision. Scientifically, this is intelligence. It's not much intelligence, but it is intelligence.

Colloquially, we say intelligence is a better decision making and complex task ability than the average human. But that's not a scientific definition. Even in IQ tests, which are widely misapplied, we still say below average humans have an intelligence score.