A regular block comment is a traditional "C-style" comment. It starts with the characters /* and ends with the characters */.
A block comment is always used for the copyright/ID comment at the beginning of each source file. It is also used to "comment out" several lines of code. Since block comments do not nest, their use in other parts of the source code would make it difficult to comment out code. Hence, the use of block comments other than for the copyright/ID comment and commenting out code is strongly discouraged.