An "insurance company" sells insurance, which is a kind of protection against bad events. For example, a health insurance company will pay for your medical bills if you get sick or injured. Common types of insurance include:
- health insurance
- car insurance
- homeowner's insurance
- life insurance (money that gets paid to someone's family if they die)
People talk about "insurance companies" like this:
The damn insurance company said that my policy didn't cover flood damage, so I didn't get anything.