PARSNIP (/pɑ:snɪp/) is an acronym that stands for "politics, alcohol, religion, sex, narcotics, -isms, and pork". These are taboo topics that are excluded from many international EFL books because of their potential to upset people, particularly powerful people, and might therefore impact sales.
Pork and alcohol make the list primarily by reason of their being banned under the Islamic religion, and are less likely to cause controversy in countries where people do not generally follow Islam. The others tend to apply more generally.
Parsnip is delectable. Good for cats, not for publishing textbooks. And may make more waves than is conducive to language learning in a classroom or group setting.