Definitions may vary of what are the human intimate or private parts, but in Western cultures they are approximately the parts involved in sexual arousal, procreation, and elimination (of feces and urine):

In some periods of Chinese history (ending in 1911), foot binding made female feet private parts.

Exposure of one's intimate parts, particularly unintended exposure, is connected with feelings of shame, and subject to strict social rules, social control and criminal justice. (See nudity and indecent exposure.)

Touching the intimate parts of another person, even through clothing, is often associated with sexual intent. Thus, if this is done without consent (or with consent that is legally not valid), it is sexual assault.

In some societies, the human intimate parts are deemed sacred and are part of cultural rituals. For example, a village in the Ivory Coast considers female genital cutting a social grace. ([1]).

See also: Sex organ, Secondary sex characteristics