This is the maximum amount that you can pay before turning the policy into a Modified Endowment Contract (MEC). The IRS like to make certain that the policy keeps with the definition of life insurance, so they set guidlines on how much money you can put into a policy before losing its favorable tax treatment.
Once a policy becomes a MEC, it stays a MEC forever any withdrawals/loans are taxed like an annuity.
Note: MEC's are not always a bad thing, especially when dealing with estate planning.
I hope that helps.