I'm currently reading about executive control, a lot of papers (e.g. Kane and Engle 2002) discuss general fluid intelligence but don't explain it. What is general fluid intelligence?
Just did some more reading, going to answer my own question:
Fluid intelligence (Gf) refers to mental operations that an individual uses when faced with a relatively novel task that cannot be performed automatically. Inductive and deductive reasoning are generally thought to be the hallmark narrow-ability indicators of Gf. Examples of Gf abilities are: Induction, Pigatian Reasoning, Quantitative Reasoning and Speed of Reasoning.
By comparison Crystallized Intelligence (Gc):
Gc refers to the breadth and depth of a persons acquired knowledge, and the application of this knowledge. Examples of Gc abilities are: Language Development, Lexical Knowledge, General Information, Information about Culture, General Science Information, Communication Abilities etc..
Reference: Reynolds, C. R., & Fletcher-Janzen, E. (2007). Encyclopedia of Special Education (Vol. 1). Wiley.
If anyone has anything better or more to add, please do.