From the Latin meaning "method of operation", modus operandi or M-O was a term that referred to one's typical methodology or means of accomplishing a task.
In 2364, Data described Dixon Hill's modus operandi as being dissimilar to that of Sherlock Holmes, after Jean-Luc Picard had described him as a 20th century version of Arthur Conan Doyle's fictional detective. (TNG: "The Big Goodbye")