Maximum Medical Improvement (MMI) is also know as fixed and stable.
It is a place in the continuum of medical care where no further improvement in an accepted medical condition is expected. Said another way, it is as good as you are going to get.
MMI is an important concept because L&I will not pay for additional medical treatment after MMI is reached. L&I takes the position that payment for medical care is no longer proper and necessary once MMI is reached. WAC296-20-01002
Keep in mind that MMI is not a fact, it is an opinion. L&I likes to push an injured worker quickly to MMI. They will do this with IME doctors.
Be sure you and your doctor advocate for the necessary and proper medical care you need to heal as well as possible.