250 characters includes all spaces, punctuation and special characters. If you have javascript enabled the form will check the description length for you.

If you receive this message Internet Explorer 6 has blocked the javascript on the page and will prevent the form from checking your character count. Click and allow the content to have the form check the description length.

You will still be able to send the form without javascript enabled but there is a risk that your description will have to be modified to fit the 250 character length.