Most states break their crimes into two major groups: felonies and misdemeanors. Whether a crime falls into one category or the other depends on the potential punishment. If a law provides for imprisonment for longer than a year, it is usually considered a felony. If the potential punishment is for a year or less, then the crime is considered a misdemeanor.
In some states, certain crimes are known as "wobblers," which means that the prosecutor may charge the crime as either a misdemeanor or a felony.
Behaviors punishable only by fine are usually not considered crimes at all, but infractions -- for example, traffic tickets. But legislatures sometimes label a behavior punishable only by fine as a misdemeanor -- such as possession of less than an ounce of marijuana for personal use in California. To learn more about the different levels of crimes, see Nolo's article Felonies, Misdemeanors, and Infractions: Classifying Crimes.