What knowledge does the system start with? A human baby starts with "Core Knowledge" (e.g., objects exist, things fall down). We need to be explicit about these.
How much practice or data does the system get? A truly intelligent system shouldn't need millions of examples to learn something simple. Humans can often learn from just one or two examples.
This is the key. How efficiently does the system turn its priors and experience into a new skill? High intelligence = high efficiency (i.e., learning fast from little data).