Round brackets ( )
are used to enclose a list of numbers to be pre- or post-multiplied or to enclose the arguments of a function; they also occur in expressions.
Square brackets [ ]
are used to enclose a list of option settings or to enclose the suffix list of a pointer; also, when preceded by $, they enclose lists of unit names or numbers for a qualified identifier.
Curly brackets { }
are each synonymous with the corresponding square bracket.