The term Nacirema (which is American spelled backwards) is originally from a magazine article by Horace Mitchell Miner. It was meant as satire in reference to sociological and anthropological study on various cultures. However, over time, the term was embraced by social scientists as a way to train students on the sociological perspective—that is, to try to examine a different culture without passing judgement upon it. This is one of the single most difficult things for anyone to do, as different cultural traits can be seen from an outsider's eyes as strange or off-putting.
In the case of Nacirema, we can essentially put the student into the position of looking at American culture from an outsider's perspective. This allows them to examine their own culture the way a member of another culture might. Take, for example, the ritual of the Nacirema men lacerating their faces each morning on a daily basis. This, of course, sounds gruesome; until the student makes the realization that the author is describing the act of shaving. Another example might be the instance in which Nacirema women "bake" their heads in individual ovens once a month as a means to increase their beauty. This would naturally sound strange to the student, until they consider what goes on at a typical salon.
The true purpose of the Nacirema satire is to teach students to put themselves into someone else's shoes and gain a better understanding that no matter how strange something may seem, cultural traits all have meaning and purpose for the culture that has created them.