Background-repeat effect is the fact that a background image will be repeated both vertically and horizontally.
You can define this mosaic effect to your blog or your desktop or other websites that you use.
Even if you're using a wordpress theme for your website, you can easily upload a seamless background to your
wordpress hosting via ftp or online editing.
It's a simple way to add a nice seamless wallpaper, texture, and the advantage is the fact that the picture is really quick to load for browser...
If you don't have hosting yet, check out hosting review communities like
Best Web Hosting Fans and
iPage Reviews.
Tutorial videos for wordpress and background editing can be found for free at
iPage Training as well as Youtube.