It refers to the rise in Indian markets in Nov-Dec, followed by a decline in January. This has happened five times in 10 years since 2003. This year, the Nifty has not risen during Nov-Dec.
So should we be expecting a rise in January?
FYI, it is the opposite in US markets, i.e. stocks prices decline in December due to profit/loss booking and rebound back in January as buyers return.