This is basically a rate that a state insurance agency puts out there to tell people what the per-unit price of insurance should be.
But no one (and by no one, we mean insurance carriers) usually even pays attention to these rates. They exist because they can be helpful to consumers and carriers, and also because states require them.
Each state has an insurance bureau specific to their state, and each state sets a standardized price "per unit" for insurance carriers in (or at least selling in) that state. This term isn't used very often anymore. Now it's more often referred to as "loss data." Basically, the bureau will collect data from every insurance selling in that state, everything from health to auto to life to property. The bureau analyzes this information, and then makes requests to the Department of Insurance (or whatever specific title that department holds in that particular state) to change the rates for particular types of insurance.
The bureau is advocating for the insurance company, while the department of insurance is consumer-focused. Here's the interesting part: insurance companies don't necessarily have to follow those rate increases. Have you ever gotten quotes for insurance, like on your car, and noticed a big difference in premium quotes? Odds are good that some of those companies are selling insurance across several states, adjusting their premiums to be more competitive in the market, and using the other states in their group to balance it out...selling some products super cheap in one state, but for a different rate in another, and using the whole group to keep the profits steady.
