If you're referring to a wildcard DNS entry, it is simply an "A" record with a "*" as the host name.
The two things you're referring to are the same if you're talking about DNS. Your terminology might be a bit off, but as far as I know, the only way to do a wildcard is in the hostname field.
Of course, you could have these:
With the second example, you've actually created a third level domain or what people often refer to as a subdomain. More often then not, though, when someone says subdomain, they're really talking about the hostname field of the domain name, as in:
With a little luck, I didn't just totally confuse you. The vernacular use of DNS terminology doesn't always match up with the same terms defined in DNS standards, though they are often the same exact words.