A plateau refers either to a piece of land that is level and located above nearby land, or the term can refer to a situation that is relatively unchanged for a period of time. In the case of an unchanged situation, the word has either a negative or a positive connotation, depending on whether change is advantageous.
A negative connotation of the word "plateau" refers to someone who wishes to see progress, such as an individual who wants to lose weight or achieve a promotion. An individual who hits a plateau in this case is unable to realize a particular goal. A positive connotation of the word "plateau" refers to a situation in which continual progression is bad, such as an illness.