In Maine, "criminal speed" means you have exceeded the speed limit by 30mph or more. For example, if the speed limit is 75 mph and you are traveling at 105 or 110mph, you have now committed a criminal offense.
This is a big deal. If you are only traveling 15mph over the limit, it is just a civil offense. It cannot be punished with jail time. There is a fine, and you will have points on your license. But if you are exceeding the speed limit by 30mph or more, you are facing the possibility of jail time. It is a Class E misdemeanor, which means you can be punished by a maximum of six months in jail and a $1000 fine. I am finding more and more that prosecutors and judges take these charges seriously. For people who have a history of speeding, there is a possibility of going to jail. If you are hitting triple digits, 100mph or greater, you are running a very high risk of facing actual jail time. It may be 48 or 72 hours, but there is a real risk there.
If you have been charged with criminal speed, it is not something to take lightly. It is a big deal, and you need to call a criminal defense attorney.