Secondary data means  Data collected by someone else earlier  Surveys, observations, experiments, questionnaire, personal interview, etc. Government publications, websites, books, journal articles, internal records etc.

And also advantage of secondary date are

• Ease of access. The secondary data sources are very easy to access. ...
• Low cost or free. ...
• Time-saving. ...
• Allow you to generate new insights from previous analysis. ...
• Longitudinal analysis. ...
• Anyone can collect the data