Liquidation ratio (LR), % - the debt/collateral ratio represents the limit after which your CDP can be liquidated.
For example, 50% means that if the debt/collateral ratio will be >50%, the position can be triggered for liquidation. LR>ICR creates a buffer to protect against instant liquidation if you borrow the maximum limit.
Liquidation ratio is basically at how high of a percentage can the actual collateralized debt position be triggered for liquidation. The risk-level of your CDP is determined by how close you are to the liquidity rate. For example, the Initial Collateral Rate (ICR) for Ether is 77%, while the liquidity rate is at 78%. Meaning that if you go ahead and use the full limit of collateral at 77% you'll be just 1% away from being liquidated. That's why you should borrow below the ICR. You can use the risk indicator at the bottom of the page to see how risky your transaction is.