I'm not sure what you mean <% is the starting tag that define an ASP script as %> is the closing tag, similar to PHP open/starting tags <?php/?> The server need those tags to identify the programming language your script is written to render the proper content. Other this, I don't know what you mean by difference between such tag and a script.
Hello, 1 .<% is used in asp for server side execution while script used for client side execution. 2. The code within <% tag is executed by IIS server while script tags are executed by browser script engine.