If a quality or feature is inbuilt, it is part of the thing itself, not added on later. A phone may have an inbuilt camera; a plan may have an inbuilt weakness; a person may have an inbuilt tendency to worry. British English likes inbuilt; American English often says built-in for objects (a built-in cupboard) and still uses inbuilt, or more often innate, for character. Though actually, for personality many careful speakers prefer inborn or innate, and keep inbuilt for things that were designed in — but people do not keep that line tidy, and you will meet inbuilt for both machines and temperaments.