When reading French dictionaries, you will often see in brackets after certain words abbreviations such as fam., pop., vulg., litt., région., arch., vieilli. These are usage markers or marques d’usage. In theory they are supposed to help the reader judge when to use or not to use certain words.
The idea is that some words or expressions may have certain connotations that should be taken into account when using them. In English we spontaneously develop an intuitive feel for when to use synonyms like loot, scratch, bread, money, ka-ching, capital.
The common problem here is that many people study book French and not the more colloquial spoken language that most people use. This is the cause of a form of linguistic shock that many language-learners experience when they have to interact with native speakers.
Although the most common problem is that of too much bookish French and not enough casual language, the opposite problem also exists. Some people who have been exposed to a lot of street language may not have learned the more polite formal language. This can have rather disastrous results, as you can well imagine.
Thus, all large dictionaries include these usage markers to show users when to use certain words properly. If a word is unmarked, you can assume that it is neutral and can be used in all circumstances. Here is a quick guide to the typical markers to be found in French dictionaries like Le petit Robert or Le petit Larousse illustré:
Vulg. This indicates vulgar or coarse language. Many of these words revolve around human anatomy, bodily functions and sexuality. You should use these words with the greatest caution. There is nothing wrong with these words. It’s just that you have to know when and, above all, when not to use them.
Interestingly, the common French word merde ‘crap’ is the equivalent of ‘break a leg’ as a form of encouragement for stage performers. A euphemism for this word is le mot de Cambronne. This refers to the reply of Napoleon’s general, Pierre Cambronne, when asked by the English to surrender at the battle of Waterloo.
Fam., pop. Words marked familier or populaire are considered rather casual or low-class without being vulgar. Words like le fric, le blé, la piastre (Quebec) are considered casual synonyms of l’argent ‘money’.
Arg. L’argot is French slang. Although close to the previous category, French argot refers specifically to the specialized language of the criminal underworld or of special groups such as prisoners or street gangs.
Litt. Literary language is quite self-explanatory. This is written vocabulary that is used only in books and on very formal occasions. For example, the passé simple tense is very common in the written language but all but absent in the spoken language. Another example is the imperfect subjunctive that can be found in 19th century and early 20th century literature.
Arch., Vieilli. Old and archaic words that have disappeared from contemporary French. They will be found in very old literature.
Région. A regionalism is a word or usage that occurs only in certain French-speaking regions and therefore not considered standard French. In Africa une essencerie is a gas station. In Quebec usage of the adjective dispendieux “expensive” would be a regionalism. It must be noted that a regionalism is always relative to some reference point. Since all major dictionaries are made in France, regionalisms are defined with reference to standard French spoken in France.