“Secondary sources analyze, review or restate information in primary resources or other secondary resources. Even sources presenting facts or descriptions about events are secondary unless they are based on direct participation or observation. Moreover, secondary sources often rely on other secondary sources and standard disciplinary methods to reach results, and they provide the principle sources of analysis about primary sources.”
Most of the sources that an aspiring Heathen will come across will fall solidly into this category – as many of the books available will have made reference to and built upon the information the relatively small number of primary sources provide. From works like The Well and the Tree to Lady with a Mead Cup to Ghosts and Godpoles: the number that fit into the secondary category is staggering as many quality books that we have deal with aspects of the worldview that utilize the extant lore in an analytical way to further our collective understanding.
Much like the understanding of primary sources aids the secondary items we read, secondary sources clarify the points of interest usually gained from tertiary sources.