A misdemeanor is a crime that the state legislature has decreed the punishment for as no more than one year in jail. A felony is a crime that the punishment for is set at more than one year in prison.
The differences between the two are set by statute when the state legislature (or in the case of Federal offenses, Congress) passes the law. Misdemeanor crimes are punishable by imprisonment for NOT...
It's a crime commited that is serious but not a felony. Such as speeding 20 miles over the speed limit, typical traffic stops. Or minor in possesion, open container, public intoxication...ect.
The generally accepted difference is the maximum sentence or penalty that was set by the legislature when it passed that law. Misdemeanors are punishable by a sentence of NOT MORE than 1 year in jail...