What @PSR and @Craig wrote.
Plus, there are two more syntax variants:
1.
type value
This form only casts constants (string literals). Like in:
SELECT date '2013-03-21';
More in the manual in the chapter Constants of Other Types.
2.
type(value)
That's the function-like syntax. Works only for types whose names are valid as function names. Like in:
SELECT date(date_as_text_col) FROM tbl;
More in the manual in the chapter Type Casts.
More comprehensive answer: