An auto insurance premium discount is a reduction of what one pays the company providing one coverage. Of course the discount would have to be for an eligible reason. What they are can vary by carrier. One of the common ones is bundling or combining policies with the same insurer (like having homeowners and car insurance with the same entity). Another one often given is for renewing the policy. Companies also reward customers many times for certain safety devices they may have on their vehicle as well as anti-theft systems, being an excellent student, not getting in an accident for a period of time, taking a qualified driving course etc.
Its worth it to take the time and find out what your carrier offers discount wise. You may not taking full advantage of what they can get do to reduce how much you pay.