Modus operandi is a 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...

 phrase, approximately translated as "mode of operation". The term is used to describe someone's habits

Habituation

Habituation can be defined as a process or as a procedure. As a process it is defined as a decrease in an elicited behavior resulting from the repeated presentation of an eliciting stimulus...

 or manner of working, their method of operating or functioning. In English

English language

English is a West Germanic language that arose in the Anglo-Saxon kingdoms of England and spread into what was to become south-east Scotland under the influence of the Anglian medieval kingdom of Northumbria...

, it is frequently shortened to M.O.

The expression is often used in police work when discussing a crime

Criminology

Criminology is the scientific study of the nature, extent, causes, and control of criminal behavior in both the individual and in society...

and addressing the methods employed by the perpetrators. It is also used in criminal profiling

Offender profiling

Offender profiling, also known as criminal profiling, is a behavioral and investigative tool that is intended to help investigators to profile unknown criminal subjects or offenders. Offender profiling is also known as criminal profiling, criminal personality profiling, criminological profiling,...

, where it can help in finding clues to the offender's psychology

Psychology

Psychology is the study of the mind and behavior. Its immediate goal is to understand individuals and groups by both establishing general principles and researching specific cases. For many, the ultimate goal of psychology is to benefit society...

. It largely consists of examining the actions used by the individual(s) to execute the crime, prevent its detection and/or facilitate escape.

In the book Criminal Investigation, B.L. Berg explains that a suspect's modus operandi can help in identification, apprehension and/or repression. An M.O. file is an orderly method of recording and coding information designed to reveal habits, traits or practices of criminal suspects. This can then be used to aid in the eventual apprehension of the suspect(s), and can also be used to determine links between crimes.