Parenthesis
They are used to give additional ditail to the lector. Those indications are never essentials.
Le RMI (Revenu Minimum d'Insertion) a été augmenté.
Other signes exists with a different role.
Brakets [...] are used to cut a citation or do an intervention into it.
Ils sont venus dire bonjour [ndlr: en français dans le texte] à leur grand-mère.
Brakets {...} are mainly used in schema.
All parenthesis, [] and {} are also used in mathematics but this is another story...