Then, there are lower level domains that sit below that, called second level domains; Examples under .com include google.com and dftba.com.

然后，还有位于其下方的较低级别的域，称为二级域； .com 下的示例包括 google.com 和 dftba.com。

Like I said, more than 300 million domain names, and that's just second level domain names, not all the sub domains.

就像我说的，超过 3 亿个域名，这只是二级域名，而不是所有的子域。