Any time there is a break in your insurance coverage, it is considered a gap. It does not matter whether the break is due to being dropped by the insurance company, allowing a policy to lapse, or canceling the coverage. If you are without auto insurance coverage, you are experiencing a gap in your insurance coverage.
A gap in your insurance coverage could mean that you do not have a car and don't need insurance. For insurance companies, the end result is that you do not have insurance coverage. When you get a vehicle and go to apply for insurance, your initial payment and rates will probably higher than someone who has had continuous coverage for a number of years.
On the other hand, receiving a notice of intent to cancel by your insurance company does not mean you are without insurance. Typically, the insurance company will notify you by mail of any changes to your policy and most insurance companies will give you a 15 to 30 day grace period to get any problems corrected before your policy terminates. Until that period expires, your coverage is still active, it is merely in jeopardy of being canceled.
On common way for a gap in your coverage to happen is during a period of transition from one insurance company to another. In this case you would notify your old insurance company that you intend to drop the olicy and then secure a new policy with your new insurance carrier. If the old policy is canceled before you have gotten your new insurance cards you are probably experiencing a break in coverage. Contact your new insurance company immediately to get verification of coverage.