A misdemeanor is an offense that can yield no more than a year in jail and requires only a conviction by trial. A felony is considered a "high crime" and is defined as an offense that can yield more than a year of prison time. Felonies require an indictment (basically a preliminary jury hearing to determine if there is sufficient evidence to go to trial), and then a conviction by trial. Felonies generally are much nastier records wise, require more time before they can be sealed or expunged (depending on state law) if they can be at all. They exclude you from certain rights such as gun ownership, voting, holding public office etc automatically. The system is fairly skewed and crimes are often made felonies in a reactionary context, i.e. some trivial computer crimes can yield felonies while cracking another mans skull under the right circumstances may only yield a misdemeanor assault charge after plea bargaining.
