There are three ways to add comment to a delphi source file:
{ This can be a single line comment }
{ but it can also span multiple lines
}
// Single line comment
The single line comment ends at the end of the line. The other comments have their own end.
(* This also can be a single comment *)
(* And it also can span multiple lines
*)
{ Can be used to comment out code containing a (* comment *)
// Or one of those
}
(* Can be used to coment out code containing a { comment }
// Or one of those
*)
// And this can contain the (* Single *) version of the { other } comments.
There is no real difference. But some people reserve one comment style to (temporary) comment out code. Because you can't nest the same type but you can nest different types.
Trivia, the (* *) comment is included to support (real) old keyboards that had no { and }. You can also use (. .) for [].