My definition of "intelligence"
D. S. Blank

First, a simple version:

intelligence - the complexity of the model that sufficiently explains
one's behavior.

a more technical one:

intelligence - the complexity of the concepts one must invoke in order
to explain the behavior of a system in a given context.

Notes and comments

Simple models could explain one's behavior with few
mechanisms. Although the behavior might be appear quite complex, the
model that explains it doesn't have to be, and therefore would have a
low intelligence.

A "lookup table" is a relatively simple model, and thus low
intelligence. Basic stimulus-response is a simple model.

"Randomness" is a simple mechanism, and therefore low intelligence
measure.

More sophisticated models might involve more complex notions, like
"memory", "representations", "plans", etc.

One can explain one's own behavior using this method, and thus have a
perception of one's own intelligence.

Problems? It is not based on cause-effect but behavior. Intelligence
is a perception; it can change with the development of the observer.

A model might involve "emergence" which is simple to explain at one
(macroscopic) level, but would actually be a complex model at the fine
(microscopic) level. Thus would have high complexity, and therefore
higher intelligence.