The Line-Continuation Symbol is a symbol that can be used to prevent confusion caused by word-wrapping in AppleScript Editor.
display dialog "Hello World!" ¬ default answer ""
Although this code takes up 2 lines, the compiler reads the first line, sees the line-continuation symbol, and then reads the second line as a continuation of the first line. Using the U.S. keyboard, this character can easily be achieved by the key combination Option-l (lowercase L). As an alternative, or for those that don't use a U.S. keyboard, you can simply use Option-Return in Script Editor and a continuation character along with a new line will be inserted.