Patent Prosecution is representing the invention’s patent application before the USPTO. It is also called patent representation. Patent Prosecution is the conducting of communications with the USPTO regarding the examination of a patent application, or a patent.
It is most frequently things like, letters to address any rejections or objections made regarding a patent application, amendments to add new or revised claims, or the conducting of examiner interviews. It also includes submitting and processing other patenting actions such as: Protests, Citation of Prior Art, Ex-Parte and Inter Partes Reexamination, and Supplemental Examination.
Patenting Costs article: How much does it cost to get a patent? $5-8k total (US Patent issued), depending on what kind (plant, design or utility), how complex, and in which countries patent protection is sought.