A background variable is a certain factor in a respondent’s background or circumstance which may affect other variables. However, such factors will not necessarily be significantly affected by the other variables.
For example, it could be that one background variable of a respondent (i.e., his religion) as it influences his food preference. However, it is unlikely that his food preference will be the variable that would dictate his religion. Hence, background variables are generally assumed to have no substantial relevance to the subject matter.