Modus operandi
A modus operandi (often shortened to M.O. or MO) is someone's habits of working, particularly in the context of business or criminal investigations, but also more generally. It is a Latin phrase, approximately translated as 'mode (or manner) of operating'.

Term
The term is often used in police work when discussing crime and addressing the methods employed by criminals. It is also used in criminal profiling, where it can help in finding clues to the offender's psychology. It largely consists of examining the actions used by the individuals to execute the crime, prevent its detection and facilitate escape. A suspect's modus operandi can assist in their identification, apprehension, or repression, and can also be used to determine links between crimes.In business, modus operandi is used to describe a firm's preferred means of executing business and interacting with other firms.

Plural
The plural is modi operandi (rather than modi operandorum). The word operandi is a gerund in the genitive case, "of operating"; gerunds can never be pluralised in Latin, as opposed to gerundives. When a noun with an attribute in the genitive is pluralised, only the head noun normally changes, just as in English with "of": "a fact of life, two facts of life" (unlike, for instance, les modes opératoires in French).

See also
Criminology – Study of crime and criminal actions/behavior
John E. Douglas – American criminal profiler
Latin phrases
Modus ponens – Rule of logical inference
Modus tollens – Rule of logical inference
Modus vivendi – Arrangement that allows conflicting parties to coexist in peace
Signature crime – crime which exhibits characteristics unique to an offender's psychologyPages displaying wikidata descriptions as a fallback

References
Further reading
External links
 The dictionary definition of modus operandi at Wiktionary