A semantic differential is a question with two opposites terms at both ends of a line.
In a survey several types of questions can be used. One of these is a semantic differential. The respondent has to give an answer on a scale white to opposite terms. Most often dots are used to collect the answer because it is more or less difficult to give or measure the answer on a continuous line.
An example makes it easier to understand what is meant:
With a sequence of this type of questions much more information can be gathered in the same time. The most difficult aspect for the editor of a semantic differential is to find terms that are really the opposite.