There is an example listed in the documentation for while that explains the syntax:
Like with the if statement, you can group multiple statements within the same while loop by surrounding a group of statements with curly braces, or by using the alternate syntax:
while (expr):
statement
...
endwhile;
An answer over here explains it like this:
This (:) operator mostly used in embedded coding of php and html.
Using this operator you can avoid use of curly brace. This operator reduce complexity in embedded coding. You can use this(:) operator with if, while, for, foreach and more...
Without (:) operator
<body>
<?php if(true){ ?>
<span>This is just test</span>
<?php } ?>
</body>
With (:) operator
<body>
<?php if(true): ?>
<span>This is just test</span>
<?php endif; ?>
</body>
