Group health insurance is when a group of people are covered under one health insurance plan. This is most commonly seen with employer-sponsored health insurance; however, self-employed individuals can also make their own health insurance group for themselves and their dependents.
Your health insurance group number identifies your group from other groups who are insured with the same insurance company. You can find this number on your insurance card.
Everyone insured with a company will be part of the same group. So, if you have employer-sponsored health insurance, you and your co-workers and their families who are all under the same insurance plan will all be part of the same group.
If you file your own claims, you will need this number in order to do so. If your doctor files your claims for you, then his office will need your health insurance group number in order to do so.