For a continuously-stocked product, an 80% CSL means that

80% of the demand will be met

there is an 80% chance that the product is in-stock when the replenishment arrives

80% of the demand will be lost

In the continuous review model, the decision on when to place a replenishment order depends on all of the following EXCEPT

the replenishment lot size

the amount of safety stock needed

the average demand

the lead time

there is a 20% chance that the product is in-stock when the replenishment arrives