Margin of error, also referred to as sampling error, describes the potential deviation of a survey result from the actual result had the entire audience, rather than a sample, been measured. Usually reported as plus or minus a particular percentage.

Margin of error is typically provided in conjunction within a confidence level. For example, a result of 75% + 5% margin of error at 95% confidence means that if the survey was repeated 100 times you could expect that 95 out of 100 times (confidence level) the response would be between 70% and 80% (margin of error.) 

See also Statistically Significant.