In flagrante delicto or sometimes simply in flagrante (Latin

Latin

Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

: "in blazing") is a legal term used to indicate that a criminal has been caught in the act of committing an offence (compare corpus delicti

Corpus delicti

Corpus delicti is a term from Western jurisprudence referring to the principle that a crime must have been proven to have occurred before a person can be convicted of committing that crime. For example, a person cannot be tried for larceny unless it can be proven that property has been stolen...

). The colloquial "caught in the act", "caught red-handed", or "caught rapid" are English equivalents.

Like many instances of the ablative case

Ablative case

In linguistics, ablative case is a name given to cases in various languages whose common characteristic is that they mark motion away from something, though the details in each language may differ...

 in Latin, the expression does not have a simple translation into English. The root phrase is the adjective flagrāns (flaming or blazing) and the noun dēlictum (offence, misdeed or crime).
The closest literal translation would be "in blazing offence", where "blazing" is a metaphor

Metaphor

A metaphor is a literary figure of speech that uses an image, story or tangible thing to represent a less tangible thing or some intangible quality or idea; e.g., "Her eyes were glistening jewels." Metaphor may also be used for any rhetorical figures of speech that achieve their effects via...

 for vigorous, highly visible action.

The Latin term is sometimes used colloquially as a euphemism

Euphemism

A euphemism is the substitution of a mild, inoffensive, relatively uncontroversial phrase for another more frank expression that might offend or otherwise suggest something unpleasant to the audience...

 for someone being caught in the act of sexual intercourse

Sexual intercourse

Sexual intercourse, also known as copulation or coitus, commonly refers to the act in which a male's penis enters a female's vagina for the purposes of sexual pleasure or reproduction. The entities may be of opposite sexes, or they may be hermaphroditic, as is the case with snails...

.