Why is there a "t" instead of "www" on the Costco website?

I was going to look something up on the Costco website this morning, but the website URL seems to be redirecting to "http://t.costco.com/" instead of "http://www.costco.com/". I haven't seen a "t" prefix like that replacing the "www" before. Does anybody know what that's about?

its just a subdomain, you can have them any name you want www. email. webmail. etc are just common naming conventions but it doesn't have to be so if you want to use t. then its fine you can even have iloveMLP-Bro. subdomain as your web site

alternatively it's part of a script that redirects requests to a different webpage.

i dont know the website but I used to do that with a dynamic dns service.

looks like the t. version has a load of hidden facebook scripting in it.. oO

You will quite often encounter a sub-domain like this.

Classic example are mobile versions of websites, for example m.cnn.com...

Thanks guys! I am used to seeing the redirects to "m." Mobile sites, but hadn't ever seen the "t" before. I was wondering if the domain may have been hijacked?