can someone explain to me what are sitewide links
heard that they negatively affect rankings

lets say i have a website xyz and abc
i then put links on every page on abc for the site xyz
is a sitewide linking with reference to seo linking say one page of a site on all pages of another website
what if i put different pages of a site on another website
will google still view this as sitewide

i.e i have xyz.com and abc.com
scenario 1
i put the page xyz.com on every page of abc.com

scenario 2
ie put 10 different pages from xyz.com on abc.com each on differnt page of abc.com as in
xyz.com on abc.com
xyz.com/1.html on abc.com/1.html e.t.c

does google penalize you with the sitewide link penalty or is it different

Sitewide links are links that appear the same in every page of a site.
In nowadays SEO nothing is goog or bad by itself. Its how you use it to determine if is good or bad. If the sidewide link is natural then everythiing is OK. If the reputation of your and the other site is good then also is OK. If you have purchased links the that is bad (depending of how ofthe and in what extend you do so).
Your 2nd senario seems to be more SEO correct.

Well, the best things you can do is go through this post over the Search Engine Watch I am pretty much sure it will help you in clearing your doubt about what actually site wide links is and are all of then unnatural.

The links which are displayed on the every pages of the website are generally referred as sitewide links. Mostly these links are placed at the footer or sidebar of a website.

Hi!

Sitewide links are links that are present on every page of your site. These links are often placed in the footer or sidebar of your site and they can be present anywhere. There is no rule that sitewide links are bad, you can look on Google's Webmaster Help.

when implementing sitewide links vary the position u place the links & also vary the title they will look more natural that way

No, itwill never affect the ranbking of your website. If you putyour website's link in every page's footer means, then it will never affect your website's ranking in any means and terms.

@larryholley, is credit link is same as sitewide link?

place <meta name="author" content="me"> where me is of course you, in the <head>, we are all using php asp etc so this is only a single edit
If the authors of abc and xyz match bots do not consider the sitelinks to be external, eg KFC and TacoBell links

left over from google's, now ended, rel=author google+ experiment

it also matters how the link is generated, a sidebar automa bla bla blah,,,,,
read Kelly's link, its better