The margin of error of a given statistic is an amount that is allowed for in case of miscalculation or change of circumstances.
It is usually the radius or half of the width of the confidence interval of that statistic.
Given that a news reporter reports the results of a survey and states that 45% of those surveyed responded "yes" with a margin of error of "plus or minus 5%."
This means that the actual percentage of the number of people that responded "yes" is between the values of (45 - 5)% and (45 + 5)%.
i.e. the actual percentage of the number of people that responded "yes" is between 40% and 50%.