TRUNCATE quickly removes all rows from a table. It has the same effect as an unqualified DELETE but since it does not actually scan the table it is faster. This is most useful on large tables.
TRUNCATE cannot be used if there are foreign-key references to the table from other tables. Checking validity in such cases would require table scans, and the whole point is not to do one.
TRUNCATE will not run any user-defined ON DELETE triggers that might exist for the table.