Microsoft's official breed of HTML as spit out by Office 97 and Office 2000. In addition to assuming the Windows-1252 character set is used by all browsers (leading to ? appearing in lieu of smart quotes and other such extended characters in Mozilla et al) it uses a perverse blend of CSS to put lots of stylistic information everywhere possible.
While MS-HTML renders just fine in Internet Explorer 5, and Mozilla can strip away most of the bloat fine, other browsers like Netscape 4 have a very hard time dealing with it. Furthermore, it is extremely large and impossible to maintain if you prefer to work in plaintext. By offloading formatting to a separate, 1 KB style sheet, I was able to reduce the size of one MS-HTML file by about 80% when converting it to straight HTML. On a corporate intranet such bloat doesn't take very long to load, but modem users will be frustrated as precise table rendering code takes eons to download.
Open Microsoft Word. Type Hello, World!. Click Save as Web Page. Choose a file name. Look at the file. It is 1.54 KB. It looks like the same as the following code:
<html>
<head>
<title>Hello, world</title>
</head>
<body>
Hello, world!
</body>
</html>
And that's for 13 characters of text.
Thanks to xriso for pointing out a typo.