So sometimes "culture" (1) is our biggest container of all for describing a particular people and everything about them: American culture. Nuclear fusion would fall into this broadest of meanings because there are some people, institutions in the larger society who are capable of nuclear fusion.
Sometimes "culture" (2) is a kind of equivalent for "ideology": the beliefs, value-systems, starting assumptions of a particular group of people. Nuclear fusion would fall within this definition of culture, just insofar as it is something that Americans think is worthwhile.
Sometimes "culture" (3), in a more limited definition, refers to certain widely shared rituals and practices that characterize one group of people and often differentiate it from other groups.
Sometimes, "culture" (4) in a different definition refers to works of literature, music, painting, sculpture. These exist inside (1) (they are produced or consumed by members of the society in question); they generally emerge from and reflect (2) the ideology of that society; they often have links to (3) the rituals and practices of the culture.
The areas mapped out by each definition can overlap, or one be nested inside the other.
Sometimes culture (5) means "high culture" in particular. Not too much any more, since we have "pop culture," and we regard it as having its own value. But a trace of this definition lingers in a descriptor like "cultured." If you call someone that, they are generally versed in the works of high-culture, not pop culture.
Mostly by culture, Civ means (4) and (5). For (1), they just use "civilization" itself. For (2), they mostly use "social policy."