The line contains several 'hacks'.
The first one is the use of "* html". Of all browsers, IE is the only one
who will read this as a viable selector, while the others just ignore it,
since everyone knows that nothing on a web page can have an ancestor for the
<html> tag.
The next one is the use of "w\idth:93px;", which (I believe) is targeted at
IE5x and its broken interpretation of the box model. All browsers except
this will see width: 91px, and ignore the second specification. IE5 sees
the first *and* the second, resulting in the width of that specified element
being set to 93px not 91px for this browser only.
The selector itself says -
"For IE only, find the <a> tag with class="slidek" which is contained within
the #container element, and set its width to 91px UNLESS you are IE5, in
which case, set its width to 93px."
This is dangerous code, in my opinion, to fix something that would be much
better handled with IE conditional comments...