use of keywords in domain name
domain extensions should be relevant to the theme of your website
url should not exceed the character limits (60 characters)
avoid usage of hyphens in the url etc.

I think, SEO friendly URL is that keywords name in domain and hyphen not used in url.

The url have Keywords in it is called as seo friendly Url.....

I don't really think URL's should be too much of a worry. Obviously if you can get a short url that is within the context of your site, that would be good. But, if you just need to make something easily remembered. Just do that.