When you create an account, you are asked whether or not you want to setup a specific domain name or show the Zigpoll on all domains. Generally, if you're not sure what this means it's safe to just select Show on all domains. But if you're still curious, let's break it down.
If you select Show on all domains it means that any of your polls can be embedded anywhere on the web, even on sites that you do not own. Normally this isn't a problem since it's unlikely someone will want to embed your poll on their website. But if you're worried about it you can lock it down by entering your domain name within this form.
If you chose to enter your domain name, you're given a choice of:
Include subdomains means that it will include all subdomains under your parent domain. So, for example, if your website is roseandrex.com this will include www.roseandrex.com, cdn.roseandrex.com, and any other subdomain you can think of.
If you want to just have your Zigpoll show up on a specific subdomain (say like blog.roseandrex.com only) then you would chose the Match Exactly option and enter blog.roseandrex.com.