It is a rewrite rule for a web server. It means that anything that is example:
/Details/12
/Details/3433
/Details/Hello
Will be redirect to a new URL
/NewsDetails.aspx?id=12
/NewsDetails.aspx?id=3433
/NewsDetails.aspx?id=Hello
It is do make human friendly URL addresses, like
what's that mean, please[
^]