What is meant by 'crimes and misdemeanors'?

Misdemeanor comes from demeanor, which means “behavior toward others” or “outward manner” (as in “his quiet demeanor”), itself derived from the verb demean, which means “to conduct or behave (oneself) usually in a proper manner”—not to be confused with the other and much more common verb demean that means “to lower in character, status, or reputation” (as in “I won’t demean myself by working for so little money”). These two verbs are spelled the same way but come from different roots.

Therefore, misdemeanor literally means “bad behavior toward others.” This led to parallel usage as both general bad behavior and legal bad behavior. In American law, a misdemeanor is “a crime less serious than a felony.” A felony is defined as “a federal crime for which the punishment may be death or imprisonment for more than a year.” As misdemeanor became more specific, crime became the more general term for any legal offense.

The phrase “high crimes and misdemeanors,” found in Article Two, Section 4 of the Constitution, has been used in English law since the 14th century, as have other fixed phrases using synonymous terms, such as “rules and regulations” and “emoluments and salaries.” It can be very difficult to distinguish between any of these pairs of words, and their frequent use together renders them less technical in today’s highly specific legal vocabulary. “High crimes” are serious crimes committed by those with some office or rank, and was used in the language describing impeachment proceedings of members of the British Parliament in the 18th century.