Carnival (known as Shrovetide in certain localities) is a festive season that occurs at the close of the Christian pre-Lenten period, consisting of Quinquagesima or Shrove Sunday, Shrove Monday, and Shrove Tuesday or Mardi Gras.

Carnival typically involves public celebrations, including events such as parades, public street parties and other entertainments, combining some elements of a circus. Elaborate costumes and masks allow people to set aside their everyday individuality and experience a heightened sense of social unity. Participants often indulge in excessive consumption of alcohol, meat, and other foods that will be forgone during upcoming Lent. Traditionally, butter, milk, and other animal products were not consumed "excessively", rather, their stock was fully consumed during Shrovetide as to reduce waste. This festival is known for being a time of great indulgence before Lent (which is a time stressing the opposite), with drinking, overeating, and various other activities of indulgence being performed. For example, pancakes, donuts, and other desserts are prepared and eaten for a final time. During Lent, dairy and animal products are eaten less, if at all, and individuals make a Lenten sacrifice, thus giving up a certain object of desire (e.g. sweets), with the money that would go to purchase what was sacrificed being donated at the church as alms for the poor.

As such, during the season of Shrovetide, it is customary for Christians to ponder what Lenten sacrifices they will make for the coming Lent. The traditions of carrying Shrovetide rods and consuming Shrovetide buns after attending church are celebrated. On the final day of the season, Shrove Tuesday, many traditional Christians, such as Lutherans, Anglicans, and Roman Catholics, "make a special point of self-examination, of considering what wrongs they need to repent, and what amendments of life or areas of spiritual growth they especially need to ask God's help in dealing with." During Shrovetide, many churches place a basket in the narthex to collect the previous year's Holy Week palm branches that were blessed and distributed during the Palm Sunday liturgies. On Shrove Tuesday (the final day of Shrovetide), churches burn these palms to make the ashes used during the services held on the very next day, Ash Wednesday.

The term "Carnival" is traditionally used in areas with a large Catholic presence, as well as in Greece. The celebration is known as Fastelavn in historically Evangelical Lutheran countries. It is called Shrovetide in areas with a high concentration of Anglicans (Church of England/US Episcopal Church), Methodists, and other Protestants. In Slavic Eastern Orthodox nations, Maslenitsa is celebrated during the last week before Great Lent. In German-speaking Europe and the Netherlands, the Carnival season traditionally opens on 11/11 (often at 11:11 a.m.). This dates back to celebrations before the Advent season or with harvest celebrations of St. Martin's Day.

The word carnival is said to come from the Late Latin expression carne levare, which means "remove meat"; a folk etymology derives it from carne vale, "farewell to meat". In either case, this signifies the approaching fast of Lent. The word carne may also be translated as flesh, producing "a farewell to the flesh", a phrase embraced by certain Carnival celebrants to embolden the festival's carefree spirit.

Other scholars argue that the origin of the word is a common meat-based country feast (in Latin carnualia) or the festival of the Navigium Isidis ("ship of Isis"), where the image of Isis was carried to the seashore to bless the start of sailing season. The festival consisted of a parade of masks following an adorned wooden boat, called in Latin carrus navalis, possibly the source of both the name and the parade floats.

The characteristics of the celebration of Carnival take their origins from ancient European festivals, such as the Greek Dionysian (the Anthesteria) or the Roman Saturnalia. During these festivities, there was a temporary release from social obligations and hierarchies to make way for the overthrow of order, joking and even debauchery. From a historical and religious point of view, the Carnival therefore represented a period of celebration, but above all of symbolic renewal, during which chaos replaced the established order, which, however, once the festive period was over, re-emerged new or renewed and guaranteed for a cycle valid until the beginning of the following Carnival.

From an anthropological point of view, Carnival is a reversal ritual, in which social roles are reversed and norms about desired behavior are suspended. During antiquity, winter was thought of as the reign of the winter spirits; these needed to be driven out in order for summer to return. Carnival can thus be regarded as a rite of passage from darkness to light, from winter to summer: a fertility celebration, the first spring festival of the new year.