You may have had enough of research and want to focus on teaching which you enjoy much more. You may want to look into different types of jobs where you can use the skills that you have learnt in graduate school, although not directly applying them. Some people may want to continue to do research but not in an academic environment. Rest assured that there are jobs, that fit all of these descriptions, available on the market. The Postdoc is usually someone within a few years of finishing their doctorate, and is still in the process of getting their research program going, so that they can compete for permanent positions at research schools.
Most postdoctoral positions are for one, two or three years.
A postdoc position usually has a reduced teaching load, and the postdoc is required to vigorously pursue their research program and to talk about it in seminars. People like Ken Ono, Adam Parusinski, Li Guo, Seva Lev, Alex Kasman, Songjie Ren, Alexander Borisov, Daniel Shiu and Wojtech Wieczorek have been recent or current postdocs in Athens. Because of the intense competition it is vital that you write a wonderful application, particularly your research plan, so that your application will get as good treatment as possible. These are usually one year positions and are usually for active researchers. They are usually open to people at all ranks, but it is likely that the pay is too low to attract senior researchers.