Insurance companies set limits on individual claims and on the aggregate of claims during a period of time. Many policies have both types of limits in force. For example, a public liability policy might have a limit of $25,000 per accident or claim and an aggregate limit of $100,000.
http://www.investopedia.com/terms/a/aggregatelimit.asp
For example, if your annual aggregate limit is $20 million, and you have $25 million worth of claims that occurred in the period, then the company would only pay up to $20 million. Aggregate means you can have multiple claims in one period, but any sum exceeding the limit would not be paid out.
http://www.investopedia.com/terms/a/aggregatelimit.asp
An aggregate deductible is the system most high-deductible health plans use for family deductibles. It works differently than the more common embedded deductible system used in non-HDHP health insurance.
https://www.verywell.com/what-is-an-aggregate-deductible-how-does-it-work-1738451
An employer is not required to issue a Form W-2 solely to report the value of the health care coverage for retirees or other employees or former employees to whom the employer would not otherwise provide a Form W-2. The chart below illustrates the types of coverage that employers must report on the Form W-2.
https://www.irs.gov/affordable-care-act/form-w-2-reporting-of-employer-sponsored-health-coverage
Employers that are subject to this requirement should report the value of the health care coverage in Box 12 of the Form W-2, with Code DD to identify the amount. There is no reporting on the Form W-3 of the total of these amounts for all the employer’s employees.
https://www.irs.gov/affordable-care-act/form-w-2-reporting-of-employer-sponsored-health-coverage
What is an 'Aggregate Limit'. An aggregate limit is a contract provision used in insurance to limit the amount that can be paid in the policy period. An aggregate limit is the maximum dollar amount your insurer will pay to settle your claims. Often, the limit is referred to as an annual aggregate limit, which is the total amount your insurer will pay in a single year.
http://www.investopedia.com/terms/a/aggregatelimit.asp
1 The health plan then begins to pay the health care expenses of the entire family.  One member of the family has high health care expenses. The amount he or she pays out-of-pocket for those expenses is large enough to meet the family’s aggregate deductible.
https://www.verywell.com/what-is-an-aggregate-deductible-how-does-it-work-1738451
There are two ways the aggregate deductible can be met: As each member of the family uses and pays for health care services, the amount they pay out-of-pocket for those services is credited toward the family’s aggregate deductible.
https://www.verywell.com/what-is-an-aggregate-deductible-how-does-it-work-1738451
Once the aggregate family deductible has been met, health insurance coverage kicks-in for the entire family. As each member of the family uses and pays for health care services, the amount they pay out-of-pocket for those services is credited toward the family’s aggregate deductible.
https://www.verywell.com/what-is-an-aggregate-deductible-how-does-it-work-1738451
The Affordable Care Act requires employers to report the cost of coverage under an employer-sponsored group health plan. Reporting the cost of health care coverage on the Form W-2 does not mean that the coverage is taxable. The value of the employer’s excludable contribution to health coverage continues to be excludable from an employee's income, and it is not taxable.
https://www.irs.gov/affordable-care-act/form-w-2-reporting-of-employer-sponsored-health-coverage
what is aggregate group health insurance
Aggregate group health insurance is that each member of the family uses and pays for health care services, the amount they pay out-of-pocket for those services is credited toward the family’s aggregate deductible. 