what do you mean by secondary analysis?

based on what I have read in the internet.Secondary analysis is a collection that brings together the key publications on the secondary analysis of data and embraces many aspects of how to analyze quantitative survey data, whether primary or secondary. As secondary analysis, defined as use of data that was collected by individuals other than the investigator, is often a starting point for other social science research methods, this set will be a critical resource for researchers across the social sciences.