A Likert scale is a psychometric scale commonly involved in research that employs questionnaires. It is the most widely used approach to scaling responses in survey research, such that the term is often used interchangeably with rating scale, or more accurately the Likert-type scale, even though the two are not synonymous.
source:
Wikipedia Article on Likert Scales
Participants that are responding to a Likert questionnaire will register their opinion on a agree/disagree scale. (eg; '1' being "absolutely disagree"; '10' being absolutely agree).