Umbrella Liability (AKA Excess Liability) provides additional coverage when the limits of insurance on an underlying policy are exceeded.  For instance, if you have $1,000,000 coverage under General Liability and you have a claim settlement for $1,500,000, the umbrella policy would pick up the additional amount.  Umbrella Liability policies add coverage to General Liability, Hired and Non-owned Auto Liability, and Employer's Liability for a single premium.  It is important to note that Umbrella coverage does not apply to the Professional Liability policy.

Umbrella liability coverage may be described in your contract in this way:  "Commercial Excess Liability Insurance in the amount of $1,000,000."