text: will someone explain what part d of medicare is specifically? i already know that it is a prescription drug plan from bush's modernization act of 2003. the terms medicare part d and medicare prescription drug coverage are interchangeable.  a beneficiary has to have medicare part a and/or part b to be eligible.  if the beneficiary already has creditable coverage, or coverage that is at least as good as medicare prescription drug coverage, then he can keep that coverage.  there's lots of info on the medicare website. http://www.medicare.gov/default.asp