A misdemeanor (also spelled misdemeanour) is any "lesser" criminal act in some common law legal systems. Misdemeanors are generally punished less severely than felonies, but theoretically more so than administrative infractions (also known as minor, petty or summary offences) and regulatory offences. Many misdemeanors are punished with monetary fines.
Contraventions are similar to misdemeanors in many civil law countries (e.g. France, Italy, Spain, Belgium, Switzerland etc.).
Read more about Misdemeanor: Distinction Between Felonies and Misdemeanors, Typical Misdemeanors and Sentences, Misdemeanor Classes, England and Wales, Northern Ireland