Function and Variable Visibility:
A) a function that is marked as internal cannot be called by other contracts, unless the function is used by a derived contract. Private Functions cannot be called by any other outside contract and public variables are generating automatically a getter function.
B) a function that is marked as external can never be called internally. Private functions can also be called by derived contracts using inheritance. Private variables are accessible also in derived contracts.

Question

Quizplus · Accepted Answer

Internal functions can be called by derived contracts, while private functions cannot be accessed by any other contract, including derived ones. Public variables automatically generate getter functions.