A postdoctoral (or post-doc) appointment is a temporary academic post held by a person who has completed his or her doctoral studies. Most postdoctoral appointments last two years, are often research-related (therefore requiring that the student possess a research doctorate, i.e. Ph.D or similar) during which time the holder has the title of research assistant or fellow and is paid a small stipend to cover living expenses.
Before entering certain fields, a post-doc appointment may be a necessary step in order to gain greater knowledge and experience, make connections, and build a name for oneself in research circles. It may also be seen as a valuable tool to distinguish oneself from other candidates when entering the job market. Such appointments are often the "stepping stone" whereby a graduate student can improve his or her publication record and hence progress to a permanent academic post.
Completion of a post-doc position does not involve the granting of an academic degree, since the doctorate by definition is the highest degree awarded in a given field.