In current genealogy practice, the adjectives primary and secondary refer to information. Primary information is given by someone who had first hand knowledge of something. Information provided by others is considered to be secondary.
Any source can have primary and secondary information, depending upon who provided it and how they came to know it. If I am with my grandmother when she dies, I may be the informant on her death certificate. The information I provide on her death would be primary information--I have first hand knowledge. The information I provide on her parents would be secondary as I do not have first hand knowledge of her birth---I wasn't there.