A felony is traditionally considered a crime of high seriousness, whereas a misdemeanor is regarded as less serious. The term "felony" originated from English common law (from the French medieval word "félonie") to describe an offense that resulted in the confiscation of a convicted person's land and goods, to which additional punishments, including capital punishment, could be added; other crimes were called misdemeanors. Following conviction of a felony in a court of law, a person may be described as a felon or a convicted felon.

In many common-law jurisdictions, such as England and Wales, Ireland, Canada, Australia, and New Zealand, crimes are no longer classified as felonies or misdemeanors. Instead, crimes are classified by mode of trial as indictable offences, triable by jury, which are usually more serious, and summary offences, triable by summary procedure without a jury, which are usually less serious.^{[citation needed]}

In some civil law jurisdictions, such as Italy and Spain, the term delict is used to describe serious offenses, a category similar to common law felony. In other nations, such as Germany, France, Belgium, and Switzerland, more serious offenses are described as 'crimes', while 'misdemeanors' or 'delicts' (or délits) are less serious. In still others, such as Brazil and Portugal, 'crimes' and 'delicts' are synonymous (more serious) and are opposed to contraventions (less serious).

In the United States, where the felony–misdemeanor distinction is still widely applied, the federal government defines a felony as a crime punishable by death or imprisonment in excess of one year. If punishable by exactly one year or less, it is classified as a misdemeanor. The classification is based upon a crime's potential sentence, so a crime remains classified as a felony even if a defendant convicted of a felony receives a sentence of one year or less. Some individual states classify crimes by other factors, such as seriousness or context.

In the United States, a felony is a crime that is punishable by death or more than one year in prison.

Under common law, felonies were crimes punishable by either death, forfeiture of property, or both. While felony charges remain serious, concerns of proportionality (i.e., that the punishment fits the crime) have since prompted legislatures to require or permit the imposition of less serious punishments, ranging from lesser terms of imprisonment to the substitution of a jail sentence or even the suspension of all incarceration contingent upon a defendant's successful completion of probation. Standards for measurement of an offense's seriousness include attempts to quantitatively estimate and compare the effects of a crime upon its specific victims or society generally.

The reform of harsh felony laws that had originated in Great Britain was deemed "one of the first fruits of liberty" after the United States became independent.

Felonies may include but are not limited to the following: