Means you do ground and flight training with an Instrument Instructor to check whether you're still safe to fly IFR.
FAR 61.57(d)
IPC is basically Instructor discretion but has to include 6 approaches, holdings and intercepting/tracking through the use of navigation sytems: generally VOR's and Airways.
Boils down to :
6 approaches every six months to stay current,
if not 6 approaches in the next 6 months with a mandatory safety pilot,
if you haven't done anything in 12 months you need an IPC
