hyperlink - Why would I put ?src= in a link? -

I dumb to not know this, but I see a lot of links in web pages and instead:

  & lt; A href = "http://foo.com/" & gt;  

... they use it:

  & lt; A href = "http://foo.com/?src=bar.com" & gt;  

Now I understand that src = something is saying that this referral is coming from barcode, but I do not understand why it should be Should anyone explicitly call out what has some light on me? Is there something that I need to include in my program generated link?

Edit : OK, sorry, I'm not quite clear. I understand GET syntax with a question mark and different parameters by ampersand I'm wondering what is this special source parameter? Why a site joins one another and why a crowd of CRCR parameters end up in the end, although there is no indication that the destination site normally uses it. For example, by rotating your mouse over the screenshot. Link URL is

but moms4mom.com is our site. Passing the Src parameter is nothing, so why is it included?

There are a few reasons that src is being used explicitly but in general, rephrase rely on To determine the referrer [SIC], it is easy and reliable to rely on a query string because later it's often broken, intentionally or not. On the other hand, browsers have never broken the query string in almost any URL, since it is very important for pages to work, as opposed to referendums, besides a referer often referring to any site without any deliberate action. That is what some users dislike.