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Abstraction and the classical definitions, plus the terminology questions asked verbatim in screens.
3 questions in CS Fundamentals.
Encapsulation, inheritance, polymorphism and abstraction are worth stating as consequences rather than definitions - what each one buys you and what it costs. Abstraction decides what a type means to its caller; encapsulation protects how that meaning is upheld.
Substitutability is a claim about behaviour, and signatures carry none of it. A subclass that rejects an argument its supertype accepted has strengthened a precondition, which the compiler cannot see: the code type-checks, and it breaks callers that were written correctly against the base type.
The compiler cannot know, so it emits an indirect call through a per-class table of function pointers that the object carries a reference to. The lookup itself is a couple of memory accesses; the real cost is the optimisations the compiler cannot perform when the target is not known until run time.