Yes. Enter as the domain names as you like, separated by a comma. Our default multidomain certificate comes with three domain names included, but you can add more - we charge around $99 per year for additional domains. We'll also show a breakdown of the price on the final step of your order.
You can also add domain names later if you need. We'll discount them based on the time left of your certificate - just log in to make the changes.
We don't limit the amount of domain names: our largest customers have around fifty domain names - and we can provide discounts for these kinds of orders if you email us. There are also well known sites with even more domain names - (check out American Airlines EV cert). A thousand domain names works in most browsers. At 10,000 domain names you'll hit response size limits.
Note we always provide 'www' for free for all certificates.