It means being good at first order predicate logic. And possibly higher order too when you consider `call/n` and lambdas. It means being good at generalization, at reasoning in causal terms, at understanding structure and grammar, at encoding problems as graphs and querying them for solutions, and much more.

Basically it's what current LLMs lack. They're good at spewing coherent text but they lack the building blocks of reason, which are made of logic, and which confer the quality of being consistent. A implies B.