One of three things, usually.

Someone who is (in decreasing order of importance, sorda) proficient with HTML, CGI programming (C, C++, Servelets, Perl, Python, etc.), Java, SQL and RDBMS, perhaps XML, JavaScript, various databasing systems (other than SQL and RDBMS), much of the TCP/IP suite of protocols (at least how to use them, if not how to implement them also), and familiar with DNS. They must also be artistically inclined, or at least understand how to make a pleasant looking website.

Someone who's proficient with HTML, maybe does a little CGI. They have their own website, they'll make you one if you pay them about as much as someone listed above sometimes. Less than 50% could go into the catagory above this one but would rather do other things or don't have the required talent and time. More than 50% are more towards the next catagory which is ...

Someone who made a website with no less than 3 frames and 10 animated gifs on the first page. They know how to use a WYSIWYG editor if they get lots of help. Some dip into HTML but most would rather not or wouldn't know how. None of this is to say that their sites don't contain interesting or relavent content though. Some aspire to higher levels but have other things they're much more interested in. Most people inthis catagory either go up to the next one or just drop the whole website thing -- it was just a fad anyway to them.