Non-response is the term generally used for the failure to give the relevant information being collected in the survey. Poor response can be because of the variety of causes, for instance, if the topic of the survey is of the intimate nature, respondents might not care to answer certain questions.
Since it is quite possible that the respondents in the survey differ in some of their characteristics from those which do not respond, a large number of non-respondents might introduce bias into the final results.