It is shorthand for "while 1 is true." Since that is always true (in Blitz "1" is a synonym for "true") you get an infinite loop. That's a pretty common way to do infinite loops in just about all programming languages. As in:
While 1
title_screen()
Wend
Then just make sure the program executes End at some point inside the loop. "End" exits the program immediately.
While 1
title_screen()
Wend
Then just make sure the program executes End at some point inside the loop. "End" exits the program immediately.