This refers to the "aggregate" limit of your general liability policy.
Look at your policy declarations and you'll likely see something like this:
- General Aggregate: $2,000,000
- Prod/Comp Ops Aggregate: $2,000,000
- Each Occurrence: $1,000,000
- Personal/Adv Injury: $1,000,000
- Fire Legal Liablity: $100,000
- Medical Payments: $5,000
A "Per Policy" aggregate means the most your insurer will pay for the total of all claims during your policy term (usually one year) is the first number - $2M.
A "Per Project" aggregate means the insurer will pay the same $2M for all claims that occur from any specific project. Frequently, the "Per Project" endorsement requires that each separate project be listed by name. Expect the insurer to charge you for a "Per Project" aggregate - it greatly increase the amount they could potentially pay during the policy term.