sentences:  Evergreening
  
  Evergreening is any of various legal, business and technological strategies by which producers extend the lifetime of their patents that are about to expire, in order to retain royalties from them, by either taking out new patents (for example over associated delivery systems, or new pharmaceutical mixtures), or by buying out, or frustrating competitors, for longer periods of time than would normally be permissible under the law.Evergreening is not a formal concept of patent law; it is best understood as a social idea used to refer to the myriad ways in which pharmaceutical patent owners use the law and related regulatory processes to extend their high-earning intellectual property rights, particularly over highly profitable (either in total sales volume or price per unit) "blockbuster" drugs.