A postdoc is supposed to be a defined period of time in which a new researcher receives advanced training, writes Julie Gould at the Nature Jobs blog. It's usually, she adds, a three-year contract and in that time, the postdoc works in the principle investigator's lab to conduct research, while honing their skills and learning how to be an independent researcher.
It seems a bit like a job, but Karen Hinxman, consultant at the Postdoc Development Centre at Imperial College, London tells Gould that "being a postdoc is not a career in itself."
Instead, Hinxman emphasizes that it is "a stepping stone to the next part of your career." Eventually, she notes, researchers won't be able to move on to the next postdoc because of age or experience restrictions on fellowships, and because they've become too expensive for PIs to employ.
It's time, then Gould says, to seek to start your own lab or look beyond academic positions.