Innate ideas are ideas or knowledge prior and independant of sense experience.
For Plato, knowledge of the Forms derives from innate ideas which are accessible to memory.
In Descartes, all principles of science and knowledge are founded on clear and distinct ideas, or incorrigible truths, which are innate in the mind and which may be captured by the method of reason.
Innate ideas came to be the focus of attack by empiricist philosophers who sought to argue that the mind is at first a tabula rasa only subsequently informed by sense experience. The classic objection to innate ideas occurs in Locke’s essay concerning Human understanding, where it is argued that if there were ideas innate in the mind then we whould expect to find them expressed by infants and untutored savages. But experience conclusively shows that it is not the case.