This time period occurs after a patent application is filed and before the patent issues and includes the back and forth between the USPTO and the inventor. In a nutshell, my current thought is that patent prosecution is a lot like the game of telephone.
Typically, an inventor tells a patent agent/attorney about their invention. They attorney (with or without) the inventor's help, writes the patent application and sends it to a patent examiner. The inventor uses technical language and the attorney overlays legalese and rewrites the technical language so that it's broad and narrow at the same time. The patent examiner reads the application and tells the attorney to tell the inventor what problems they've found. The USPTO almost always finds problems.
The examiner reads and responds using a form book that starts out with very exciting language like...
Claims 1, 2, 4 and 15 are rejected under 35 U.S.C. 102(b) as being anticipated by Jones (US 24,584)...This sentence simply means the patent examiner thinks Jones thought of the things in claims 1, 2, 4, and 15 first.
Writing patents and examining them is complex work, and I'm drawn to the complexities of doing this work.